80C32/80C52/80C32E
5
Rev. J
– July 03, 2000
Port Pin
Alternate Function
P3.0
P3.1
P3.2
P3.3
P3.4
P3.5
P3.6
P3.7
RXD (serial input port)
TXD (serial output port)
INT0 (external interrupt 0)
INT1 (external interrupt 1)
TD (Timer 0 external input)
T1 (Timer 1 external input)
WR (external Data Memory write strobe)
RD (external Data Memory read strobe)
Port 3 can sink/source three LS TTL inputs. It can drive CMOS inputs without external pullups.
4.7. RST
A high level on this for two machine cycles while the oscillator is running resets the device. An internal pull-down
resistor permits Power-On reset using only a capacitor connected to VCC. As soon as the Reset is applied (Vin), PORT
1, 2 and 3 are tied to one. This operation is achieved asynchronously even if the oscillator does not start-up.
4.8. ALE
Address Latch Enable output for latching the low byte of the address during accesses to external memory. ALE is
activated as though for this purpose at a constant rate of 1/6 the oscillator frequency except during an external data
memory access at which time one ALE pulse is skipped. ALE can sink/source 8 LS TTL inputs. It can drive CMOS
inputs without an external pullup.
4.9. PSEN
Program Store Enable output is the read strobe to external Program Memory. PSEN is activated twice each machine
cycle during fetches from external Program Memory. (However, when executing out of external Program Memory, two
activations of PSEN are skipped during each access to external Data Memory). PSEN is not activated during fetches
from internal Program Memory. PSEN can sink/source 8 LS TTL inputs. It can drive CMOS inputs without an external
pullup.
4.10. EA
When EA is held high, the CPU executes out of internal Program Memory (unless the Program Counter exceeds 1
FFFH). When EA is held low, the CPU executes only out of external Program Memory. EA must not be floated.
4.11. XTAL1
Input to the inverting amplifier that forms the oscillator. Receives the external oscillator signal when an external
oscillator is used.
Output of the inverting amplifier that forms the oscillator. This pin should be floated when an external oscillator is used.