Philips Semiconductors Preliminary data
P89C51RA2/RB2/RC2/RD2xx80C51 8-bit Flash microcontroller family
8KB/16KB/32KB/64KB ISP/IAP Flash with 512B/512B/512B/1KB RAM
2002 Jul 18
7
PIN DESCRIPTIONS
PIN NUMBER
PDIP PLCC LQFP
V
SS
20 22 16 I Ground: 0 V reference.
V
CC
40 44 38 I Power Supply: This is the power supply voltage for normal, idle, and power-down
operation.
P0.0–0.7 39–32 43–36 37–30 I/O Port 0: Port 0 is an open-drain, bidirectional I/O port. Port 0 pins that have 1s
written to them float and can be used as high-impedance inputs. Port 0 is also the
multiplexed low-order address and data bus during accesses to external program
and data memory. In this application, it uses strong internal pull-ups when emitting 1s.
P1.0–P1.7 1–8 2–9 40–44,
1–3
I/O Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pull-ups on all pins.
Port 1 pins that have 1s written to them are pulled high by the internal pull-ups and
can be used as inputs. As inputs, port 1 pins that are externally pulled low will
source current because of the internal pull-ups. (See DC Electrical Characteristics:
I
IL
).
Alternate functions for P89C51RA2/RB2/RC2/RD2xx Port 1 include:
1 2 40 I/O T2 (P1.0): Timer/Counter 2 external count input/Clockout (see Programmable
Clock-Out)
2 3 41 I T2EX (P1.1): Timer/Counter 2 Reload/Capture/Direction Control
3 4 42 I ECI (P1.2): External Clock Input to the PCA
4 5 43 I/O CEX0 (P1.3): Capture/Compare External I/O for PCA module 0
5 6 44 I/O CEX1 (P1.4): Capture/Compare External I/O for PCA module 1
6 7 1 I/O CEX2 (P1.5): Capture/Compare External I/O for PCA module 2
7 8 2 I/O CEX3 (P1.6): Capture/Compare External I/O for PCA module 3
8 9 3 I/O CEX4 (P1.7): Capture/Compare External I/O for PCA module 4
P2.0–P2.7 21–28 24–31 18–25 I/O Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. Port 2 pins that
have 1s written to them are pulled high by the internal pull-ups and can be used as
inputs. As inputs, port 2 pins that are externally being pulled low will source current
because of the internal pull-ups. (See DC Electrical Characteristics: I
IL
). Port 2
emits the high-order address byte during fetches from external program memory
and during accesses to external data memory that use 16-bit addresses (MOVX
@DPTR). In this application, it uses strong internal pull-ups when emitting 1s.
During accesses to external data memory that use 8-bit addresses (MOV @Ri),
port 2 emits the contents of the P2 special function register.
P3.0–P3.7 10–17 11,
13–19
5, 7–13 I/O Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. Port 3 pins that
have 1s written to them are pulled high by the internal pull-ups and can be used as
inputs. As inputs, port 3 pins that are externally being pulled low will source current
because of the pull-ups. (See DC Electrical Characteristics: I
IL
). Port 3 also serves
the special features of the P89C51RA2/RB2/RC2/RD2xx, as listed below:
10 11 5 I RxD (P3.0): Serial input port
11 13 7 O TxD (P3.1): Serial output port
12 14 8 I INT0 (P3.2): External interrupt
13 15 9 I INT1 (P3.3): External interrupt
14 16 10 I T0 (P3.4): Timer 0 external input
15 17 11 I T1 (P3.5): Timer 1 external input
16 18 12 O WR (P3.6): External data memory write strobe
17 19 13 O RD (P3.7): External data memory read strobe
RST 9 10 4 I Reset: A high on this pin for two machine cycles while the oscillator is running,
resets the device. An internal resistor to V
SS
permits a power-on reset using only
an external capacitor to V
CC
.
ALE 30 33 27 O Address Latch Enable: Output pulse for latching the low byte of the address
during an access to external memory. In normal operation, ALE is emitted twice
every machine cycle, and can be used for external timing or clocking. Note that one
ALE pulse is skipped during each access to external data memory. ALE can be
disabled by setting SFR auxiliary.0. With this bit set, ALE will be active only during a
MOVX instruction.
