TSC87C52
Port 3 also serves the functions of various special features of the TEMIC’s C51 Family, as listed below:
Port Pin
P3.0
P3.1
P3.2
P3.3
P3.4
P3.5
P3.6
P3.7
Alternate Function
RxD (serial input port)
TxD (serial output port)
INT0 (external interrupt 0)
INT1 (external interrupt 1)
T0 (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.
Some Port 3 pins receive control signals during EPROM programming and program verification.
RST
A high level on this pin 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 V
CC
. The port pins will be driven to their reset
condition when a minimum VIH1 voltage is applied whether the oscillator is started or not (asynchronous reset).
ALE/PROG
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 external pullup.
If desired, to reduce EMI, ALE operation can be disabled by setting bit 0 of SFR location 8Eh (MSCON). With this
bit set, the pin is weakly pulled high. However, ALE remains active during MOVX, MOVC instructions and external
fetches. Setting the ALE disable bit has no effect if the microcontroller is in external execution mode (EA=0).
Throughout the remainder of this datasheet, ALE will refer to the signal coming out of the ALE/PROG pin, and the
pin will be referred to as the ALE/PROG pin.
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.
EA/VPP
External Access enable. EA must be strapped to VSS in order to enable the device to fetch code from external Program
Memory locations 0000h to FFFFh. Note however, that if any of the Security bits are programmed, EA will be internally
latched on reset.
EA should be strapped to VCC for internal program execution.
This pin also receives the programming supply voltage (VPP) during EPROM programming.
XTAL1
Input to the inverting amplifier that forms the oscillator. Receives the external oscillator signal when an external
oscillator is used.
XTAL2
Output from the inverting amplifier that forms the oscillator. This pin should be floated when an external oscillator
is used.
MATRA MHS
Rev. C – 10 Sept 1997
5
Preliminary
TEMIC [ TEMIC SEMICONDUCTORS ]
