W78C32C/W78C032C
5. FUNCTIONAL DESCRIPTION
The W78C032C architecture consists of a core controller surrounded by various registers, four
general purpose I/O ports, 256 bytes of RAM, three timer/counters, and a serial port. The processor
supports 111 different instruction and references both a 64K program address space and a 64K data
storage space.
5.1
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 W78C31. Timer 2 is a special feature of
the W78C032C: 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.
5.2
Clock
The W78C032C is designed to be used with either a crystal oscillator or an external clock. Internally,
the clock is divided by two before it is used. This makes the W78C032C relatively insensitive to duty
cycle variations in the clock.
5.2.1
Crystal Oscillator
The W78C032C incorporates a built-in crystal oscillator. To make the oscillator work, a crystal must
be connected across pins XTAL1 and XTAL2. In addition, a load capacitor must be connected from
each pin to ground, and a resistor must also be connected from XTAL1 to XTAL2 to provide a DC bias
when the crystal frequency is above 24 MHz.
5.2.2
External Clock
An external clock should be connected to pin XTAL1. Pin XTAL2 should be left unconnected. The
XTAL1 input is a CMOS-type input, as required by the crystal oscillator. As a result, the external clock
signal should have an input one level of greater than 3.5 volts.
5.3
5.3.1
Power Management
Idle Mode
The idle mode is entered by setting the IDL bit in the PCON register. In the idle mode, the internal
clock to the processor is stopped. The peripherals and the interrupt logic continue to be clocked. The
processor will exit idle mode when either an interrupt or a reset occurs.
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