W78E516B
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AUX-RAM 0H−255H is addressed indirectly as the same way to access external data memory with
the MOVX instruction. Address pointer are R0 and R1 of the selected register bank and DPTR
register. An access to external data memory locations higher than 255H will be performed with the
MOVX instruction in the same way as in the 8051. The AUX-RAM is disable after a reset. Setting
the bit 4 in CHPCON register will enable the access to AUX-RAM. When AUX-RAM is enabled the
instructions of "MOVX @Ri" will always access to on-chip AUX-RAM. When executing from internal
program memory, an access to AUX-RAM will not affect the Ports P0, P2, WR and RD .
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 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.
Clock
The W78E516B is designed with either a crystal oscillator or an external clock. Internally, the clock is
divided by two before it is used by default. This makes the W78E516B relatively insensitive to duty
cycle variations in the clock.
Crystal Oscillator
The W78E516B 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.
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.
Power Management
Idle Mode
Setting the IDL bit in the PCON register enters the idle mode. 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.
Power-down Mode
When the PD bit in the PCON register is set, the processor enters the power-down mode. In this
mode all of the clocks are stopped, including the oscillator. To exit from power-down mode is by a
hardware reset or external interrupts INT0 to
INT1
when enabled and set to level triggered.
Reduce EMI Emission
The W78E516B allows user to diminish the gain of on-chip oscillator amplifier by using programmer
Publication Release Date: February 2000
Revision A3
-5-
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