W77C32 datasheet(21/78 Pages) WINBOND

21 / 78 page

W77C32/W77C032A

Publication Release Date: February 1, 2007

- 21 -

Revision A8

SBUF1.7-0: Serial data of the serial port 1 is read from or written to this location. It actually consists of

two separate 8-bit registers. One is the receive resister, and the other is the transmit

buffer. Any read access gets data from the receive data buffer, while write accesses are

to the transmit data buffer.

ROMMAP

Bit:

Mnemonic: ROMMAP

Address: C2h

WS:

Wait State Signal Enable. Setting this bit enables the WAIT signal on P4.0. The

device will sample the wait state control signal WAIT via P4.0 during MOVX

instruction. This bit is time access protected

Power Management Register

Bit:

CD1

CD0

SWB

XTOFF

ALE-OFF

DME0

Mnemonic: PMR

Address: C4h

CD1, CD0: Clock Divide Control. These bit selects the number of clocks required to generate one

machine cycle. There are three modes including divide by 4, 64 or 1024. Switching

between modes must first go back devide by 4 mode. For instance, to go from 64 to 1024

clocks/machine cycle the device must first go from 64 to 4 clocks/machine cycle, and then

from 4 to 1024 clocks/machine cycle.

CD1,

CD0

Clocks/machine cycle

Reserved

1024

SWB:

Switchback Enable. Setting this bit allows an enabled external interrupt or serial port activity

to force the CD1,CD0 to divide by 4 state (0,1). The device will switch modes at the start of

the jump to interrupt service routine while a external interrupt is enabled and actually

recongnized by microcontroller. While a serial port reception, the switchback occurs at the

start of the instruction following the falling edge of the start bit.

XTOFF: Crystal Oscillator Disable. Setting this bit disables the external crystal oscillator. This bit can

only be set to 1 while the microcontroller is operating from the RC oscillator. Clearing this bit

restarts the crystal oscillator, the XTUP (STATUS.4) bit will be set after crystal oscillator

warmed-up has completed.

ALEOFF: This bit disables the expression of the ALE signal on the device pin during all on-board

program and data memory accesses. External memory accesses will automatically enable

ALE independent of ALEOFF.

0 = ALE expression is enable;

1 = ALE expression is disable

DME0:

This bit determines the on-chip MOVX SRAM to be enabled or disabled.

Set this bit to 1 will enable the on-chip 1KB MOVX SRAM.

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