W78C54

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1. INT2 / INT3

Two additional external interrupts, INT2 and INT3, whose functions are similar to those of external

interrupt 0 and 1 in the standard 80C52. The functions/status of these interrupts are

determined/shown by the bits in the XICON (External Interrupt Control) register. The XICON register

is bit-addressable but is not a standard register in the standard 80C52. Its address is at 0C0H. To

set/clear bits in the XICON register, one can use the "SETB (/CLR) bit" instruction. For example,

"SETB 0C2H" sets the EX2 bit of XICON.

2. PORT4

Another bit-address port P4 is also available except only 4 bits (P4<3:0>) can be used. This port

address is located at 0D8H with the same function as that of port P1,except the P4.3 and P4.2 are

alternative function pins. It can be used as general I/O pins or external interrupt input sources

(INT2/INT3).

Example:

P4

REG

0D8H

MOV

P4, #0AH

; Output data "A" through P4.0

−P4.3.

MOV

A, P4

; Read P4 status to Accumulator.

SETB

P4.0

; Set bit P4.0

CLR

P4.1

; Clear bit P4.1

Reduce EMI Emission

Because of the large on-chip mask-ROM, when a program is running in internal ROM space, the ALE

will be unused. The transition of ALE will cause noise, so it can be turned off to reduce the EMI

emission if it is useless. Turning off the ALE signal transition only requires setting the bit 0 of the

AUXR SFR, which is located at 08Eh. When ALE is turned off, it will be reactivated when the program

accesses external ROM/RAM data or jumps to execute an external ROM code. The ALE signal will

turn off again after it has been completely accessed or the program returns to internal ROM code

space..

POF Flag

bit can be set/cleared by software allowing a user to determine if the reset is the result of a power-on

or a warm up by external reset. To avoid effect of POF flag, the power voltage must remain above

3V.

Timers 0, 1, and 2

Timers 0, 1, and 2 each consist of two 8-bit data registers. These are called TL0 and TH0 for Timer 0,

TL1 and TH1 for Timer 1, and TL2 and TH2 for Timer 2. The TCON and TMOD registers provide

control functions for timers 0, 1. The T2CON register provides control functions for Timer 2. RCAP2H

and RCAP2L are used as reload/capture registers for Timer 2.

The operations of Timer 0 and Timer 1 are the same as in the W78C51. Timer 2 is a special feature

of the W78C52C: it is a 16-bit timer/counter that is configured and controlled by the T2CON register.

Like Timers 0 and 1, Timer 2 can operate as either an external event counter or as an internal timer,

depending on the setting of bit C/T2 in T2CON. Timer 2 has three operating modes: capture, auto-

reload, and baud rate generator. The clock speed at capture or auto-reload mode is the same as that

of Timers 0 and 1.