(R) Understanding FLEX 6000 Timing May 1999, ver. 2 Introduction Application Note 92 Altera(R) devices provide predictable performance that is consistent from simulation to application. Before configuring a device, you can determine the worst-case timing delays for any design by using the MAX+PLUS(R) II Timing Analyzer. You can also calculate the propagation delays by using the timing model provided in this application note along with the timing parameters listed in the FLEX 6000 Programmable Logic Device Family Data Sheet in this data book. 1 For the most precise timing results, you should use the MAX+PLUS II Timing Analyzer, which accounts for the effects of secondary factors such as placement and fan-out. This application note defines FLEX(R) 6000 device internal and external timing parameters, and illustrates the timing model for the FLEX 6000 device family. Familiarity with the FLEX 6000 architecture and characteristics is assumed. Refer to the FLEX 6000 Programmable Logic Device Family Data Sheet for a complete description of the FLEX 6000 architecture and for specific values for timing parameters listed in this application note. Internal Timing Microparameters The timing delays contributed by individual FLEX 6000 architectural elements are called internal timing microparameters, which cannot be measured explicitly. All internal timing microparameters are shown in italic type. The following sections define the internal timing microparameters for the FLEX 6000 device family. I/O Element Timing Microparameters The following list describes the I/O element (IOE) timing microparameters for the FLEX 6000 device family: Altera Corporation A-AN-092-02 tOD1 Output buffer and pad delay with the slow slew rate logic option turned off and VCCIO = VCCINT. tOD2 Output buffer and pad delay with the slow slew rate logic option turned off and VCCIO = low voltage. 919 AN 92: Understanding FLEX 6000 Timing tOD3 Output buffer and pad delay with the slow slew rate logic option turned on. tXZ Output buffer disable delay. The delay required for high impedance to appear at the output pin after the tri-state buffer's enable control is disabled. tZX1 Output buffer enable delay with the slow slew rate logic option turned off and VCCIO = VCCINT. The delay required for the output signal to appear at the output pin after the tri-state buffer's enable control is enabled. tZX2 Output buffer enable delay with the slow slew rate logic option turned off and VCCIO = low voltage. The delay required for the output signal to appear at the output pin after the tri-state buffer's enable control is enabled. tZX3 Output buffer enable delay with the slow slew rate logic option turned on. The delay required for the output signal to appear at the output pin after the tri-state buffer's enable control is enabled. tIOE Output enable control delay. The delay for a signal used to control the output enable of the IOE's tri-state buffer. tIN Input pad and buffer to FastTrack(R) Interconnect delay. The time required for a signal on an I/O pin, used as an input, to reach a row or column channel of the FastTrack Interconnect. tIN_DELAY Input pad and buffer to FastTrack Interconnect delay with additional delay turned on. The time required for a signal on an I/O pin, used as an input, to reach a row or column channel of the FastTrack Interconnect. Interconnect Timing Microparameters The following list describes the routing timing microparameters for the FLEX 6000 device family: tLOCAL 920 Logic array block (LAB) local interconnect delay. The delay incurred by a signal entering an LAB or by a signal routed between logic elements (LEs) by local routing. Altera Corporation AN 92: Understanding FLEX 6000 Timing tROW Row interconnect routing delay. The delay incurred by a signal that requires routing through a row channel in the FastTrack Interconnect. The tROW delay is a function of fan-out and the distance between the source and destination LEs. The value shown in the FLEX 6000 Programmable Logic Device Family Data Sheet is the longest delay possible for an LE with a fan-out of four LEs. However, the value generated by the MAX+PLUS II Timing Analyzer is more accurate because it includes fan-out considerations and the relative locations of the source and destination LEs of the design. 1 tCOL Column interconnect routing delay. The delay incurred by a signal that requires routing through a column channel in the FastTrack Interconnect. The value shown in the FLEX 6000 Programmable Logic Device Family Data Sheet is the longest delay possible for an LE with a fan-out of four LEs. However, the value generated by the MAX+PLUS II Timing Analyzer is more accurate because it includes fan-out considerations and the relative locations of the source and destination LEs of the design. 1 tDIN_D Altera Corporation This parameter is a worst-case value for typical applications. Post-compilation timing simulation and timing analysis are required to determine actual worst-case performance. This parameter is a worst-case value for typical applications. Post-compilation timing simulation and timing analysis are required to determine actual worst-case performance. Dedicated input to LE data delay. The time required for a signal, used as a data input, to reach an LE from a dedicated input pin. The tDIN_D delay is a function of fan-out and the distance between the source pin and destination LEs. The value shown in the FLEX 6000 Programmable Logic Device Family Data Sheet is the longest delay possible for a dedicated input with a fan-out of four LEs. However, the value generated by the MAX+PLUS II Timing Analyzer is more accurate because it includes fan-out considerations and the relative locations of the source and destination LEs of the design. 921 AN 92: Understanding FLEX 6000 Timing 1 tDIN_C Dedicated input to LE control delay. The delay of a signal coming from a dedicated input pin that is used as an LE register control signal. These LE register control signals include the clock, clear, and preset inputs to the LE register. tLEGLOBAL LE output to LE control via internally generated global signal delay. The delay incurred by a signal that routes from the output of an LE to an LE register control signal via an internally generated global signal. These LE register control signals include the clock, clear, and preset inputs to the LE register. 1 922 This parameter is a worst-case value for typical applications. Post-compilation timing simulation and timing analysis are required to determine actual worst-case performance. This parameter is a worst-case value for typical applications. Post-compilation timing simulation and timing analysis are required to determine actual worst-case performance. tLABCARRY Routing delay for the carry-out signal of an LE driving the carry-in signal of a different LE in a different LAB. A carry chain longer than one LAB skips either from one even-numbered LAB to another even-numbered LAB, or from one odd-numbered LAB to another oddnumbered LAB. tLABCASC Routing delay for the cascade-out signal of an LE driving the cascade-in signal of a different LE in a different LAB. A cascade chain longer than one LAB skips either from one even-numbered LAB to another even-numbered LAB, or from one odd-numbered LAB to another odd-numbered LAB. Altera Corporation AN 92: Understanding FLEX 6000 Timing Logic Element Timing Microparameters The following list describes the LE timing microparameters for the FLEX 6000 device family: Altera Corporation tREG_TO_REG Look-up table (LUT) delay for LE register feedback in counter mode. The delay incurred by a signal that is routed from the data output of an LE register back to the data input of the same LE register. The first LE of a counter implemented with carry chains incurs a tREG_TO_REG delay. tCASC_TO_REG Cascade-in to register delay. The delay from the cascade-in signal to the data input of the LE register. tCARRY_TO_REG Carry-in to register delay. The delay from the carry-in signal to the data input of the LE register. tDATA_TO_REG LE input to register delay. The delay from the LE data input signal through the LUT to the data input of the LE register. tCASC_TO_OUT Cascade-in to LE output delay. The delay from the cascade-in signal to the output of the LE. tCARRY_TO_OUT Carry-in to LE output delay. The delay from the carry-in signal to the output of the LE. tDATA_TO_OUT LE input to LE output delay. The time required for an LE data input signal to propagate through the LUT, bypass the register, and arrive at the output of the LE. tREG_TO_OUT Register output to LE output delay. The delay from the output of the LE register to the output of the LE. tSU LE register setup time before clock. The minimum time that the data input signal is required to be stable at the LE register input before the register clock's rising edge to ensure that the register correctly stores the input data. tSU is also the minimum recovery time between deasserting the clear signal and the rising edge of the clock. tH LE register hold time after clock. The minimum time that a signal is required to be stable at the LE register input after the register clock's rising edge to ensure that the register correctly stores the input data. 923 AN 92: Understanding FLEX 6000 Timing tCO LE register clock-to-output delay. The delay from the rising edge of the LE register's clock to the time the data appears at the register output. tCLR LE register clear delay. The delay from the assertion of the LE register's asynchronous clear input to the time the register output stabilizes at a logic low. tC LE register control signal delay. The time required for a signal to be routed to the clock, preset, or clear input of an LE register. tLD_CLR Synchronous load or clear delay in counter mode. The delay from the input of the LAB-wide synchronous clear or load signal to the data input of the register in counter mode. tCARRY_TO_CARRY Carry-in to carry-out delay. The delay incurred by generating a carry-out signal that uses the carry-in signal from the previous LE. 924 tREG_TO_CARRY Register output to carry-out delay. The delay incurred by generating a carry-out signal from the output of the register. tDATA_TO_CARRY LE input to carry-out delay. The delay incurred by generating a carry-out signal from a data input signal of the LE. tCARRY_TO_CASC Carry-in to cascade-out delay. The delay incurred by generating a cascade-out signal from the carry-in signal from the previous LE. tCASC_TO_CASC Cascade-in to cascade-out delay. The delay incurred by generating a cascade-out signal that uses the cascade-in signal from the previous LE. tREG_TO_CASC Register-out to cascade-out delay. The delay from the output of the LE register to the cascade-out signal. tDATA_TO_CASC LE input to cascade-out delay. The delay from a data input of the LE to the cascade-out signal. tCH Minimum LE register clock high time. The minimum time that the register's clock input must remain at a stable logic high state before the falling edge of the clock. Altera Corporation AN 92: Understanding FLEX 6000 Timing tCL External Timing Parameters Minimum LE register clock low time. The minimum time that the register's clock input must remain at a stable logic low state before the rising edge of the clock. External timing parameters represent actual pin-to-pin timing characteristics. Each external timing parameter consists of a combination of internal delay elements. They are worst-case values, derived from extensive performance measurements, and they are ensured by device testing or characterization. All external timing parameters are shown in bold type. For example, t1 is the AC operating specification. Other external timing parameters can be estimated by using the timing model or the equations in "Calculating Timing Delays" on page 928. External Reference Timing Parameters The following list describes the external reference timing parameters for the FLEX 6000 device family: t1 This timing parameter shows the delay of a registerto-register test pattern. There are 12 LEs including the source and destination registers. The row and column interconnects between the registers have various lengths. This timing parameter is used to determine the speed grade of FLEX 6000 devices. External Timing Parameters The following list describes the external timing parameters for the FLEX 6000 device family. Altera Corporation tINSU Setup time with global clock into LE register on the same row in column nearest to the I/O. The time required for a signal to be stable at the input pin before a rising edge is applied to the global clock pin to ensure that the register correctly stores the input data. The data input of the LE register is driven by an input pin in the same row. tINH Hold time with global clock from an I/O pin to any LE register. The time required for a signal to be stable at the input pin after a rising edge is applied to the global clock pin to ensure that the register correctly stores the input data. This parameter does not include the optional increased input delay. 925 AN 92: Understanding FLEX 6000 Timing FLEX 6000 Timing Model 926 tOUTCO Clock-to-output delay with global clock with LE register using a FastFLEXTM I/O pin. The delay from when a rising edge is applied to the global clock pin to the time the data appears at the FastFLEX I/O pin. A FastFLEX I/O pin is a row or column output pin that receives its data signals from the adjacent local interconnect driven by an adjacent LE. tODH Output data hold time after clock. The minimum time a registered output pin will remain at its previous value after a rising edge is applied to the clock input pin. This parameter applies for both global and nonglobal clocking of LE registers. Timing models are simplified block diagrams that illustrate the propagation delays through Altera devices. Logic can be implemented on different paths. You can trace the actual paths used in your device by examining the equations listed in the MAX+PLUS II Report File (.rpt) for the project. Add the appropriate internal timing parameters to calculate the approximate propagation delays through the device. However, the MAX+PLUS II Timing Analyzer provides the most accurate timing information. Figure 1 shows the FLEX 6000 timing model. Altera Corporation AN 92: Understanding FLEX 6000 Timing Figure 1. FLEX 6000 Timing Model tROW Carry-In from Previous LE tLOCAL Cascade-In from Previous LE tCASC_TO_OUT tCARRY_TO_OUT tDATA_TO_OUT tREG_TO_OUT tSU tH tCO tCLR tREG_TO_REG tCASC_TO_REG tCARRY_TO_REG tDATA_TO_REG tCOL tC tLD_CLR tLEGLOBAL tCARRY_TO_CARRY tREG_TO_CARRY tDATA_TO_CARRY tDIN_D tLABCARRY tCARRY_TO_CASC tCASC_TO_CASC tREG_TO_CASC tDATA_TO_CASC LE tLABCASC tDIN_C Carry-out to Carry-out to Next LE in Next LE in Same LAB Next LAB tIOE Cascade-out Cascade-out to Next LE in to Next LE in Same LAB Next LAB I/O Pin tOD1 tOD2 tOD3 tXZ tZX1 tZX2 tZX3 tIN tIN_DELAY IOE Altera Corporation 927 AN 92: Understanding FLEX 6000 Timing Calculating Timing Delays You can calculate approximate pin-to-pin timing delays for FLEX 6000 devices using the timing model shown in Figure 1 along with the internal timing parameters in the FLEX 6000 Programmable Logic Device Family Data Sheet in this data book. Each external timing parameter is calculated from a combination of internal timing parameters. Figure 2 shows the FLEX 6000 device family external timing parameters. For simplicity, the external parameters that contain output pin delays are shown with FastFLEX I/O pins. A FastFLEX I/O pin is a row or column output pin that receives its data signals from the adjacent local interconnect driven by an adjacent LE. To calculate the routing delays for pins that do not use the FastFLEX I/O feature, add the following delays: Add a tROW delay for row output pins driven by non-adjacent LEs in the same row. This delay also applies to column output pins driven by non-adjacent LEs in the nearest row. Add a tCOL + tROW delay for all other routing paths. To calculate the delay for a signal that follows a different path, refer to the timing model to determine which internal timing parameters to sum. Figure 2. Logic Element External Timing Parameters (Part 1 of 4) Combinatorial Delay From Row I/O Inputs: Row I/O Row or Column FastFLEX I/O Combinatorial Logic tCOMB = tIN + tROW + tLOCAL + tDATA_TO_OUT + tLOCAL + tOD1 From Dedicated Inputs: Dedicated Input Row or Column FastFLEX I/O Combinatorial Logic tCOMB = tDIN_D + tLOCAL + tDATA_TO_OUT + tLOCAL + tOD1 Clock-to-Output Delay from a Global Clock to Any Output Row or Column FastFLEX I/O Dedicated Clock LE Register tCO 928 = tDIN_C + tCO + tREG_TO_OUT + tLOCAL + tOD1 Altera Corporation AN 92: Understanding FLEX 6000 Timing Figure 2. Logic Element External Timing Parameters (Part 2 of 4) Tri-State Enable/Disable Delay tXZ or tZX From Row I/O Inputs through Logic: Row I/O tXZ, tZX = Combinatoral Logic Row or Column FastFLEX I/O tIN + tROW + tLOCAL +tDATA_TO_OUT + tLOCAL + tIOE + (tXZ or tZX1) Directly from Dedicated Inputs: Dedicated Input Row or Column FastFLEX I/O tXZ, tZX = tDIN_D + tLOCAL + tIOE + (tXZ or tZX1) Directly from Row I/O Inputs: Row I/O Row or Column FastFLEX I/O tXZ, tZX = tIN + tROW + tLOCAL + tIOE + (tXZ or tZX1) From an LE Register: Dedicated Input Row or Column FastFLEX I/O LE Register tXZ, tZX = tDIN_C + tCO + tREG_TO_OUT + tLOCAL + tIOE + (tXZ or tZX1) Altera Corporation 929 AN 92: Understanding FLEX 6000 Timing Figure 2. Logic Element External Timing Parameters (Part 3 of 4) LE Register Clear & Preset (NOT Gate Push-Back) Time From Row I/O Inputs to Locally Routed Row or Column Outputs: tCLR Row or Column FastFLEX I/O Row I/O LE Register tPRE Row or Column FastFLEX I/O Row I/O LE Register tCLR = tPRE = tIN + tROW + tLOCAL + tC + tCLR + tREG_TO_OUT + tLOCAL + tOD1 From Dedicated Inputs to Locally Routed Row or Column Outputs: tCLR Row or Column FastFLEX I/O Dedicated Input LE Register tPRE Row or Column FastFLEX I/O Dedicated Input LE Register tCLR 930 = tPRE = tDIN_C + tCLR + tREG_TO_OUT + tLOCAL + tOD1 Altera Corporation AN 92: Understanding FLEX 6000 Timing Figure 2. Logic Element External Timing Parameters (Part 4 of 4) Setup Time from a Global Clock & Row I/O Data Input Row I/O Combinatorial Logic Dedicated Clock tSU = LE Register [(tIN + tROW + tLOCAL + tDATA_TO_REG) - (tDIN_C + tC)] + tSU Hold Time from a Global Clock & Row I/O Data Input Row I/O Combinatorial Logic Dedicated Clock tH = LE Register [(tDIN_C + tC) - (tIN + tROW + tLOCAL + tDATA_TO_REG)] + tH Timing Model vs. MAX+PLUS II Timing Analyzer Hand calculations based on the timing model provide a good estimate of a design's performance. However, the MAX+PLUS II Timing Analyzer always provides the most accurate information on the performance of a design because it takes into account three secondary factors that influence the routing microparameters: Fan-out for each signal in the delay path Positions of other loads relative to the source and destination Distance between signal source and destination Fan-Out The more loads a signal has to drive, the longer the delay across tROW, tCOL, and tDIN_D. These delays are functions of the number of LABs that a signal source must drive. Load Distribution The load distribution relative to the source and destination also affects the tROW, tCOL, and tDIN_D delays. Consider a signal s1 that feeds destination d1 and logic elements y[4..1]. If y[4..1] are in different LABs, s1 has four additional loads. However, if the LEs are all in the same LAB, s1 has one shorter-delay load. Therefore, the row interconnect delay from s1 to d1 is greater when each load y[4..1] is in a different LAB. Figure 3 illustrates how variations in the position of d1 and the distribution of y[4..1] change the routing delay. Altera Corporation 931 AN 92: Understanding FLEX 6000 Timing Figure 3. Delay from s1 to d1 as a Function of Relative Position & Load Distribution Shorter Delay Longer Delay s1 d1 y1 y2 y3 y4 LAB LAB LAB s1 y1 y2 y3 y4 d1 LAB LAB LAB s1 d1 y1 y2 y3 y4 LAB LAB LAB LAB LAB LAB s1 y1 y2 y3 y4 d1 LAB LAB LAB LAB LAB LAB Distance The distance between the source and destination LEs also affects the tROW, tCOL, and tDIN_D parameters. For example, if s1 drives an LE in the same row, the delay from s1 to the LE increases as the distance from s1 to the LE increases. 932 Altera Corporation AN 92: Understanding FLEX 6000 Timing Examples The following examples show how to use internal timing microparameters to estimate the delays for real applications. Example 1: 4-Bit Equality Comparator with a Cascade Chain You can analyze the timing delays for circuits that have been subjected to minimization and logic synthesis. The synthesized equations are available in your project's MAX+PLUS II Report File (.rpt). These equations are structured so that you can quickly determine the logic implementation of any signal. For example, Figure 4 shows a 4-bit equality comparator. Figure 4. 4-Bit Equality Comparator Circuit a0 CASCADE b0 a1 b1 a2 b2 eq a3 b3 Altera Corporation 933 AN 92: Understanding FLEX 6000 Timing The MAX+PLUS II Report File for the circuit shown in Figure 4 gives the equations for eq, the output of the comparator: eq _LC3_B1 _EQ002C _EQ002 = = = = _LC2_B1 = _EQ001C = _EQ001 = _LC3_B1; LCELL( _EQ002C); _EQ002 & CASCADE( _EQ001C); a2 & a3 & b2 & b3 # a2 & !a3 & b2 & !b3 # !a2 & a3 & !b2 & b3 # !a2 & !a3 & !b2 & !b3; LCELL( _EQ001C); _EQ001; a0 & a1 & b0 & b1 # a0 & !a1 & b0 & !b1 # !a0 & a1 & !b0 & b1 # !a0 & !a1 & !b0 & !b1; Figure 5 shows a synthesized 4-bit equality comparator. Figure 5. Synthesized 4-Bit Equality Comparator _LC2_B1 a0 b0 a1 LUT _EQ001C b1 _LC3_B1 a2 b2 a3 b3 _EQ002C LUT _EQ002 eq The output pin eq is the output of the second LE of a cascade chain. The LUT of _LC2_B1 implements the comparison of the first two bits. The comparison of the second two bits is implemented in the LUT of _LC3_B1. The outputs of these two LUTs are then cascaded together to form the output of _LC3_B1. If a2 and eq are both row I/O pins, the timing delay from a2 to eq can be estimated by adding the following microparameters: tIN + tROW + tLOCAL + tDATA_TO_OUT + tROW + tLOCAL + tOD1 934 Altera Corporation AN 92: Understanding FLEX 6000 Timing If a0 is a row I/O pin, the timing delay from a0 to eq can be estimated by adding the following microparameters: tIN + tROW + tLOCAL + tDATA_TO_CASC + tCASC_TO_OUT + tROW + tLOCAL + tOD1 Example 2: 3-Bit Adder Using a Carry Chain FLEX 6000 devices have specialized resources that implement complex arithmetic functions. For instance, adders and counters require a carry function to determine whether or not to increment the next significant bit. The FLEX 6000 architecture has a built-in carry chain that performs this function. This example explains how to estimate the delay for a 3-bit adder that uses a carry chain (see Figure 6). Figure 6. 3-Bit Adder Implemented with a Carry Chain a0 sum0 b0 CARRY a1 sum1 b1 CARRY a2 sum2 b2 CARRY cout Altera Corporation 935 AN 92: Understanding FLEX 6000 Timing The MAX+PLUS II Report File contains the following equations for the 3-bit adder in Figure 6: cout sum0 sum1 sum2 _LC2_B1 _EQ001 = = = = = = _LC2_B1_CARRY _EQ002 _LC3_B1 _EQ003 = = = = _LC3_B1_CARRY _EQ004 = = _LC4_B1 _EQ005 = = _LC5_B1 _LC4_B1_CARRY _EQ006 = = = _LC5_B1; _LC2_B1; _LC3_B1; _LC4_B1; LCELL( _EQ001); !a0 & b0 # a0 & !b0; CARRY( _EQ002); a0 & b0; LCELL( _EQ003); a1 & !b1 & !_LC2_B1_CARRY # !a1 & !b1 & _LC2_B1_CARRY # a1 & b1 & _LC2_B1_CARRY # !a1 & b1 & !_LC2_B1_CARRY; CARRY( _EQ004); a1 & _LC2_B1_CARRY # a1 & b1 # b1 & _LC2_B1_CARRY; LCELL( _EQ005); a2 & !b2 & !_LC3_B1_CARRY # !a2 & !b2 & _LC3_B1_CARRY # a2 & b2 & _LC3_B1_CARRY # !a2 & b2 & !_LC3_B1_CARRY; LCELL( _LC4_B1_CARRY); CARRY( _EQ006); a2 & _LC3_B1_CARRY # a2 & b2 # b2 & _LC3_B1_CARRY; Figure 7 shows a synthesized 3-bit adder. 936 Altera Corporation AN 92: Understanding FLEX 6000 Timing Figure 7. Synthesized 3-Bit Adder _LC2_B1 a0 b0 LUT Carry Chain _EQ001 sum0 _LC2_B1_CARRY _LC3_B1 a1 b1 LUT Carry Chain _EQ003 sum1 _LC3_B1_CARRY _LC4_B1 a2 b2 LUT Carry Chain _EQ005 sum2 _LC4_B1_CARRY _LC5_B1 LUT cout In Figure 7, LE _LC2_B1 generates sum0 and a carry-out signal (_LC2_B1_CARRY) that feeds the carry-in of _LC3_B1. LE _LC3_B1 generates sum1 and a carry-out signal (_LC3_B1_CARRY) that feeds the carry-in of _LC4_B1. LE _LC4_B1 generates sum2 and cout using a2, b2, and _LC3_B1_CARRY. The cout signal must pass through _LC5_B1 because a carry buffer cannot directly feed a pin. Altera Corporation 937 AN 92: Understanding FLEX 6000 Timing If a0 and sum1 are row I/O pins, the timing delay from a0 to sum1 can be estimated by adding the following microparameters: tIN + tROW + tLOCAL + tDATA_TO_CARRY + tCARRY_TO_OUT + tROW + tLOCAL + tOD1 If a0 and cout are row I/O pins, the timing delay from a0 to cout can be estimated by adding the following microparameters: tIN + tROW + tLOCAL + tDATA_TO_CARRY + tCARRY_TO_CARRY + tCARRY_TO_CARRY + tCARRY_TO_OUT + tROW + tLOCAL + tOD1 Conclusion 938 The FLEX 6000 device architecture has predictable internal timing delays that can be estimated based on signal synthesis and placement. The MAX+PLUS II Timing Analyzer provides the most accurate timing information. However, you can also use the FLEX 6000 timing model along with the timing parameters listed in the FLEX 6000 Programmable Logic Device Family Data Sheet in this data book to estimate a design's performance before compilation. Both methods enable you to accurately predict your design's in-system timing performance. Altera Corporation Copyright (c) 1995, 1996, 1997, 1998, 1999 Altera Corporation, 101 Innovation Drive, San Jose, CA 95134, USA, all rights reserved. By accessing this information, you agree to be bound by the terms of Altera's Legal Notice.