W78LE812
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
TL2 TH2
T2 (P1.0)
1/2
TR2 (T2CON.2)
T2EX (P1.1)
RCAP2L
RCAP2H
EXF2
T2CON.6
Timer 2
Interrupt
EXEN2 (T2CON.3)
Timer 2 Clock-Out Mode
TIMER 2 MODE CONTROL
Bit:
7
-
6
5
-
4
-
3
-
2
-
1
T2OE
0
-
-
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.
Publication Release Date: February 1999
- 5 -
Revision A2
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