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N80C51GB

CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLER

Intel 

8XC51GB

ALTERNATE PORT FUNCTIONS

Ports 0 1 2 3 4 and 5 have alternate functions as well as their I O function as described below

Port Pin

P0 0 ADO–P0 7 AD7

P1 0 T2

P1 1 T2EX

P1 2 ECI

P1 3 CEXO–P1 7 CEX4

P2 0 A8–P2 7 A15

P3 0 RXD

P3 1 TXD

P3 2 INT0

P3 3 INT1

P3 4 T0

P3 5 T1

P3 6 WR

P3 7 RD

P4 0 SEPCLK

P4 1 SEPDAT

P4 2 ECI1

P4 3 C1EX0–P4 7 C1EX4

P5 2 INT2–P5 6 INT6

Alternate Function

Multiplexed Address Data for External Memory

Timer 2 External Clock Input Clock-Out

Timer 2 Reload Capture Direction Control

PCA External Clock Input

PCA Capture Input Compare PWM Output

High Byte of Address for External Memory

Serial Port Input

Serial Port Output

External Interrupt 0

External Interrupt 1

Timer 0 External Clock Input

Timer 1 External Clock Input

Write Strobe for External Memory

Read Strobe for External Memory

Clock Source for Serial Expansion Port

Data I O for the Serial Expansion Port

PCA1 External Clock Input

PCA1 Capture Input Compare PWM Output

External Interrupt INT2 – INT6

RST Reset input A low on this pin for two machine

cycles while the oscillator is running resets the de-

vice The port pins will be driven to their reset condi-

tion when a voltage below VIL max voltage is ap-

plied whether the oscillator is running or not An

internal pullup resistor permits a power-on reset with

only a capacitor connected to VSS

ALE PROG Address Latch Enable output pulse for

latching the low byte of the address during accesses

to external memory This pin (ALE PROG) is also

the program pulse input during programming of the

87C51GB

In normal operation ALE is emitted at a constant

rate of the oscillator frequency and may be used

for external timing or clocking purposes Note how-

ever that one ALE pulse is skipped during each ac-

cess to external Data Memory

If desired ALE operation can be disabled by setting

bit 0 of SFR location 8EH With this bit set the pin is

weakly pulled high However the ALE disable fea-

ture will be suspended during a MOVX or MOVC in-

struction idle mode power down mode and ICE

mode The ALE disable feature will be terminated by

reset When the ALE disable feature is suspended or

terminated the ALE pin will no longer be pulled up

weakly Setting the ALE-disable bit has no affect if

the microcontroller is in external execution mode

Throughout the remainder of this data sheet 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 is the read strobe to

external Program Memory

When the 8XC51GB is executing code from external

Program Memory PSEN is activated twice each ma-

chine cycle except that two PSEN activations are

skipped during each access to external Data Memo-

ry

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 1FFFH Note however that if either of the

Program Lock bits are programmed EA will be inter-

nally latched on reset

EA should be strapped to VCC for internal program

executions

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