®
Altera Corporation 919
Understanding
FLEX 6000 Timing
May 1999, ver. 2 Application Note 92
A-AN-092-02
Introduction
Altera
®
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
®
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
®
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
Micropara-
meters
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:
t
OD1
Output buffer and pad delay with the slow slew rate
logic option turned off and V
CCIO
= V
CCINT
.
t
OD2
Output buffer and pad delay with the slow slew rate
logic option turned off and V
CCIO
= low voltage.
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AN 92: Understanding FLEX 6000 Timing
t
OD3
Output buffer and pad delay with the slow slew rate
logic option turned on.
t
XZ
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.
t
ZX1
Output buffer enable delay with the slow slew rate
logic option turned off and V
CCIO
= V
CCINT
. The delay
required for the output signal to appear at the output
pin after the tri-state buffer’s enable control is
enabled.
t
ZX2
Output buffer enable delay with the slow slew rate
logic option turned off and V
CCIO
= 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.
t
ZX3
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.
t
IOE
Output enable control delay. The delay for a signal
used to control the output enable of the IOE’s tri-state
buffer.
t
IN
Input pad and buffer to FastTrack
®
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.
t
IN_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:
t
LOCAL
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.
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t
ROW
Row interconnect routing delay. The delay incurred
by a signal that requires routing through a row
channel in the FastTrack Interconnect. The
t
ROW
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
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.
t
COL
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
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.
t
DIN_D
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
t
DIN_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.
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1
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.
t
DIN_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.
t
LEGLOBAL
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
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.
t
LABCARRY
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 odd-
numbered LAB.
t
LABCASC
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.
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Logic Element Timing Microparameters
The following list describes the LE timing microparameters for the
FLEX 6000 device family:
t
REG_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
t
REG_TO_REG
delay.
t
CASC_TO_REG
Cascade-in to register delay. The delay from the
cascade-in signal to the data input of the LE register.
t
CARRY_TO_REG
Carry-in to register delay. The delay from the carry-in
signal to the data input of the LE register.
t
DATA_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.
t
CASC_TO_OUT
Cascade-in to LE output delay. The delay from the
cascade-in signal to the output of the LE.
t
CARRY_TO_OUT
Carry-in to LE output delay. The delay from the
carry-in signal to the output of the LE.
t
DATA_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.
t
REG_TO_OUT
Register output to LE output delay. The delay from
the output of the LE register to the output of the LE.
t
SU
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.
t
SU
is also the minimum recovery time between
deasserting the clear signal and the rising edge of the
clock.
t
H
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.
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t
CO
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.
t
CLR
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.
t
C
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.
t
LD_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.
t
CARRY_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.
t
REG_TO_CARRY
Register output to carry-out delay. The delay incurred
by generating a carry-out signal from the output of
the register.
t
DATA_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.
t
CARRY_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.
t
CASC_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.
t
REG_TO_CASC
Register-out to cascade-out delay. The delay from the
output of the LE register to the cascade-out signal.
t
DATA_TO_CASC
LE input to cascade-out delay. The delay from a data
input of the LE to the cascade-out signal.
t
CH
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.
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t
CL
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
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,
t
1
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:
t
1
This timing parameter shows the delay of a register-
to-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.
t
INSU
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.
t
INH
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.
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t
OUTCO
Clock-to-output delay with global clock with LE
register using a FastFLEX
™
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.
t
ODH
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 non-
global clocking of LE registers.
FLEX 6000
Timing Model
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.
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Figure 1. FLEX 6000 Timing Model
t
LABCARRY
t
LABCASC
t
LOCAL
t
ROW
t
COL
t
DIN_D
t
DIN_C
Carry-out to
Next LE in
Same LAB
Carry-out to
Next LE in
Next LAB
Cascade-out
to Next LE in
Same LAB
Cascade-out
to Next LE in
Next LAB
Carry-In from
Previous LE Cascade-In from
Previous LE
IOE
LE
I/O Pin
t
CARRY_TO_CASC
t
CASC_TO_CASC
t
REG_TO_CASC
t
DATA_TO_CASC
t
CARRY_TO_CARRY
t
REG_TO_CARRY
t
DATA_TO_CARRY
t
REG_TO_REG
t
CASC_TO_REG
t
CARRY_TO_REG
t
DATA_TO_REG
t
C
t
LD_CLR
t
SU
t
H
t
CO
t
CLR
t
CASC_TO_OUT
t
CARRY_TO_OUT
t
DATA_TO_OUT
t
REG_TO_OUT
t
LEGLOBAL
t
OD1
t
OD2
t
OD3
t
XZ
t
ZX1
t
ZX2
t
ZX3
t
IOE
t
IN
t
IN_DELAY
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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:
tCOMB =
t
IN
+
t
ROW
+
t
LOCAL
+
t
DATA_TO_OUT
+
t
LOCAL
+
t
OD1
From Dedicated Inputs:
tCOMB =
t
DIN_D
+
t
LOCAL
+
t
DATA_TO_OUT
+
t
LOCAL
+
t
OD1
Clock-to-Output Delay from a Global Clock to Any Output
tCO =
t
DIN_C
+
t
CO
+
t
REG_TO_OUT
+
t
LOCAL
+
t
OD1
Row or Column FastFLEX I/O
Combinatorial
Logic
Dedicated Input
Dedicated Clock
LE Register
Row or Column FastFLEX I/O
Row or Column FastFLEX I/O
Row I/O Combinatorial
Logic
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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:
tXZ, tZX =
t
IN
+
t
ROW
+
t
LOCAL
+
t
DATA_TO_OUT
+
t
LOCAL
+
t
IOE
+ (
t
XZ
or
t
ZX1
)
Directly from Dedicated Inputs:
tXZ, tZX =
t
DIN_D
+
t
LOCAL
+
t
IOE
+ (
t
XZ
or
t
ZX1
)
Directly from Row I/O Inputs:
tXZ, tZX =
t
IN
+
t
ROW
+
t
LOCAL
+
t
IOE
+ (
t
XZ
or
t
ZX1
)
From an LE Register:
tXZ, tZX =
t
DIN_C
+
t
CO
+
t
REG_TO_OUT
+
t
LOCAL
+
t
IOE
+ (
t
XZ
or
t
ZX1
)
Combinatoral
Logic
Row I/O
Dedicated Input
Row or Column FastFLEX I/O
Row I/O
Dedicated Input
Row or Column FastFLEX I/O
Row or Column FastFLEX I/O
Row or Column FastFLEX I/O
LE Register
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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
tPRE
tCLR = tPRE =
t
IN
+
t
ROW
+
t
LOCAL
+
t
C
+
t
CLR
+ t
REG_TO_OUT
+
t
LOCAL
+
t
OD1
From Dedicated Inputs to Locally Routed Row or Column Outputs:
tCLR
tPRE
tCLR = tPRE =
t
DIN_C
+
t
CLR
+ t
REG_TO_OUT
+
t
LOCAL
+
t
OD1
Dedicated Input
Row or Column FastFLEX I/O
LE Register
Row or Column FastFLEX I/O
LE Register
Row I/O
Row or Column FastFLEX I/O
LE Register
Row or Column FastFLEX I/O
LE Register
Row I/O
Dedicated Input
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Figure 2. Logic Element External Timing Parameters (Part 4 of 4)
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.
Setup Time from a Global Clock & Row I/O Data Input
tSU = [(
t
IN
+
t
ROW
+
t
LOCAL
+
t
DATA_TO_REG
) – (
t
DIN_C
+ t
C
)] +
t
SU
Hold Time from a Global Clock & Row I/O Data Input
tH= [(
t
DIN_C
+ t
C
) – (
t
IN
+
t
ROW
+
t
LOCAL
+
t
DATA_TO_REG
)] +
t
H
Row I/O
Dedicated Clock
LE Register
Combinatorial
Logic
Row I/O
Dedicated Clock
LE Register
Combinatorial
Logic
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Figure 3. Delay from s1 to d1 as a Function of Relative Position & Load Distribution
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.
Shorter Delay
Longer Delay
s1
LAB
d1y4y3y2y1s1
y1
y2
y3
y4
d1
LAB LAB
LAB LAB LAB LAB LAB LAB
d1
y1
y2
y3
y4
s1
LAB LAB LAB
s1 y4y3y2y1d1
LAB LAB LAB LAB LAB LAB
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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
CASCADE
a0
b0
a1
b1
a2
b2
a3
b3
eq
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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;
_LC3_B1 = LCELL( _EQ002C);
_EQ002C = _EQ002 & CASCADE( _EQ001C);
_EQ002 = a2 & a3 & b2 & b3
# a2 & !a3 & b2 & !b3
# !a2 & a3 & !b2 & b3
# !a2 & !a3 & !b2 & !b3;
_LC2_B1 = LCELL( _EQ001C);
_EQ001C = _EQ001;
_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
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
a0
b0
_EQ002
a1
b1
LUT
a2
b2
a3
b3
LUT eq
_EQ001C
_EQ002C
_LC3_B1
_LC2_B1
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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
b0
CARRY
a0 sum0
CARRY
b1
a1 sum1
CARRY
b2
a2 sum2
cout
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The MAX+PLUS II Report File contains the following equations for the
3-bit adder in Figure 6:
cout = _LC5_B1;
sum0 = _LC2_B1;
sum1 = _LC3_B1;
sum2 = _LC4_B1;
_LC2_B1 = LCELL( _EQ001);
_EQ001 = !a0 & b0
# a0 & !b0;
_LC2_B1_CARRY = CARRY( _EQ002);
_EQ002 = a0 & b0;
_LC3_B1 = LCELL( _EQ003);
_EQ003 = a1 & !b1 & !_LC2_B1_CARRY
# !a1 & !b1 & _LC2_B1_CARRY
# a1 & b1 & _LC2_B1_CARRY
# !a1 & b1 & !_LC2_B1_CARRY;
_LC3_B1_CARRY = CARRY( _EQ004);
_EQ004 = a1 & _LC2_B1_CARRY
# a1 & b1
# b1 & _LC2_B1_CARRY;
_LC4_B1 = LCELL( _EQ005);
_EQ005 = a2 & !b2 & !_LC3_B1_CARRY
# !a2 & !b2 & _LC3_B1_CARRY
# a2 & b2 & _LC3_B1_CARRY
# !a2 & b2 & !_LC3_B1_CARRY;
_LC5_B1 = LCELL( _LC4_B1_CARRY);
_LC4_B1_CARRY = CARRY( _EQ006);
_EQ006 = a2 & _LC3_B1_CARRY
# a2 & b2
# b2 & _LC3_B1_CARRY;
Figure 7 shows a synthesized 3-bit adder.
Altera Corporation 937
AN 92: Understanding FLEX 6000 Timing
Figure 7. Synthesized 3-Bit Adder
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.
a0
b0
_LC2_B1
sum0
_EQ001
LUT
Carry Chain _LC2_B1_CARRY
sum1
a1
_LC3_B1
b1 LUT
Carry Chain _LC3_B1_CARRY
_EQ003
_LC5_B1
cout
LUT
sum2
a2
_LC4_B1
b2 LUT
Carry Chain _LC4_B1_CARRY
_EQ005
938 Altera Corporation
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 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.
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