W78LE812

Publication Release Date: February 1999

- 5 -

Revision A2

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. In

the auto-reload mode, Timer 2 performs a up counter which is similar with standard 8052. When

counting up, an overflow in Timer 2 will cause a reload from RCAP2H and RCAP2L registers. The

Timer 2 also provides a programmable clock-out mode as a clock generator. To enable this mode,

timer 2 has to be configured with a 16-bit auto-reload timer (C/T2 = 0, CP/RL2 = 0) and bit T2OE

(T2MOD.1) must be set to 1. This mode produces a 50% duty cycle clock output and timer 2 roll-

overs will not generate an interrupt. The clock-out frequency depends on the oscillator frequency and

the reload value of registers RCAP2H and RCAP2L. The clock-out frequency is determined by

following equation:

Clock-out Frequency = Oscillator Frequency / [ 4

× ( 65536 - RCAP2H, RCAP2L ) ]

OSC

1/2

T2 (P1.0)

T2CON.6

TR2 (T2CON.2)

T2EX (P1.1)

EXEN2 (T2CON.3)

EXF2

Timer 2

Interrupt

TH2

TL2

RCAP2H

RCAP2L

1/2

Timer 2 Clock-Out Mode

TIMER 2 MODE CONTROL

Bit:

7

6

5

4

3

2

1

0

-

-

-

-

-

-

T2OE

-

Mnemonic: T2MOD

Address: C9h

T2OE: Timer 2 Output Enable. This bit enables/disables the Timer 2 clock-out function.

I/O Port Options

The Port 0 and Port 3 of W78LE812 may be configured with different types by setting the bits of the

Port Options Register POR that is located at 86H. The pins of Port 0 can be configured with either

the open drain or standard port with internal pull-up. By the default, Port 0 is an open drain bi-

directional I/O port. When the PUP bit in the POR register is set, the pins of Port 0 will perform a

quasi-bi-directional I/O port with internal pull-up that is structurally the same as Port 2. The high

nibble of Port 3 (P3.4 to P3.7) can be selected to serve the direct LED displays drive outputs by

setting the HDx bit in the PO register. When the HDx bit is set, the corresponding pin P3.x can sink

about 20mA current for driving LED display directly. After reset, the POR register is cleared and the

pins of Ports 0 and 3 are the same as those of the standard 80C31. The POR register is shown below.