AT87F52
3
The AT87F52 provides the following standard features: 8K
bytes of QuickF lash, 25 6 bytes of RAM, 32 I/ O lines, three
16-bit timer/counters, a six-vector two-level interrupt archi-
tecture, a f ull duplex serial port, on-chip oscillator, and
clock circuitry. In addition, the AT87F52 is designed with
static logic for oper ation down to zero frequency and sup-
ports tw o software sele ctable power saving mo des. The
Idle Mode stops the CPU while allowing the RAM,
timer/c oun ters, seri al p or t, and int er rupt s ystem to co nti nue
functioning. The Power Down Mode saves the RAM con-
tents but freezes the oscillator, disabling all other chip func-
tions until the next hardware reset.
Pin Description
VCC
Supply voltage.
GND
Ground.
Port 0
Port 0 is an 8-bi t open drain bidirectional I/O port. As an
output port, each pin can sink eight TTL inputs. When 1s
are written to port 0 pins, the pins can be used as high-
impedance inputs.
Port 0 can also be configured to be the multiplexed l ow-
order address/data bus during accesses to external pr o-
gram and data memory. In this mode, P0 has internal pul-
lups.
Port 0 als o rece ives the c ode byte s dur ing Qui ckFlas h pro-
grammin g a nd outputs th e c od e by te s dur in g p ro gr am ve ri -
fication. External pullups are required during program verifi-
cation.
Port 1
Port 1 is a n 8- bit bi dire ction al I/O por t with inter nal pullu ps.
The Port 1 output buffers can sink/source four TTL inputs.
When 1s are writte n to Port 1 pi ns, they ar e pulled hi gh by
the internal pullups and can be us ed as inputs. As i nputs,
Port 1 pins that are externally being pulled low will source
current (IIL) because of the internal pullups.
In addition, P1.0 and P1.1 can be configured to be the
timer/counter 2 external count input (P1.0/T2) and the
timer/counter 2 trigger input (P1.1/T2EX), respectivel y, as
shown in the following table.
Port 1 also receives the low-order address bytes during
QuickFlash programming and verification.
Port 2
Port 2 is an 8-bit bi directiona l I/O port with interna l pullups.
The Port 2 output buffers can sink/source four TTL inputs.
When 1s a re writte n to Po rt 2 pi ns, th ey a re pulle d hi gh b y
the internal pullups and can be used as inputs. As inputs,
Port 2 pins that are externally being pulled low will source
current (IIL) because of the internal pullups.
Port 2 emits the high-order address byte during fetches
from external program memory and during accesses to
external da ta m emory that u se 16 -b it a ddres s es ( MO VX @
DPTR). In this application, Port 2 uses strong internal pul-
lups when emitting 1s. During accesses to external data
memory that use 8-bit addresses (MOVX @ RI), Port 2
emits the contents of the P2 Special Function Register.
Port 2 also receives the high-order address bits and some
control signals during QuickFlash programming and verifi-
cation.
Port 3
Port 3 is an 8-bit bi directiona l I/O port with interna l pullups.
The Port 3 output buffers can sink/source four TTL inputs.
When 1s a re writte n to Po rt 3 pi ns, th ey a re pulle d hi gh b y
the internal pullups and can be used as inputs. As inputs,
Port 3 pins that are externally being pulled low will source
current (IIL) because of the pullups.
Port 3 also s erves the funct ions of var ious s peci al featu res
of the AT89C51, as shown in the following table.
Port 3 also receives some control signals for QuickFlash
programming and verification.
RST
Reset input. A high on this pin for two machine cycles while
the oscillator is running resets the device.
ALE/PROG
Address Latch Enabl e is an output pulse for latching the
low byte of the address during accesses to external mem-
ory . Thi s pi n is also t h e pr og ra m pu l se in p ut (PROG) during
QuickFlash programming.
In normal operation, ALE is emitted at a constant rate of 1/6
the oscillator frequency and may be used for external tim-
ing or clocking purposes. Note, however, that one ALE
Port Pin Alternate Functions
P1.0 T2 (external count input to Timer/Counter 2),
clock-out
P1.1 T2EX (Timer/Counter 2 capture/reload trigger
and direction control)
Port Pin Alternate Functions
P3.0 RXD (serial input port)
P3.1 TXD (serial output port)
P3.2 INT0 (external interrupt 0)
P3.3 INT1 (external interrupt 1)
P3.4 T0 (timer 0 external input)
P3.5 T1 (timer 1 external input)
P3.6 WR (external data memory write strobe)
P3.7 RD (external data memory read strobe)