W77C58 Datasheet, PDF (19/71 Pages) Winbond – 8 BIT MICROCONTROLLER

Preliminary W77C58
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
00
01
10
11
Clocks/machine cycle
Reserved
4
64
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.
Status Register
Bit:
7
6
5
4
3
2
1
0
PIP
HIP
LIP XTUP SPTA1 SPRA1 SPTA0 SPRA0
Mnemonic: STATUS
Address: C5h
PIP: Power Fail Priority Interrupt Status. When set, this bit indicates that power-fail interrupt is
currently serviced. It will be cleared when program executes the corresponding RETI
instruction.
HIP: High Priority Interrupt Status. When set, it indicates that software is servicing a high priority
interrupt. This bit will be cleared when the program executes the corresponding RETI
instruction.
LIP: Low Priority Interrupt Status. When set, it indicates that software is servicing a low priority
interrupt. This bit will be cleared when the program executes the corresponding RETI
instruction.
XTUP: Crystal Oscillator Warm-up Status. This bit indicates CPU has detected clock to be
ready. Each time the crystal oscillator is restarted by exit from power down mode or the
XTOFF bit is set, hardware will clear this bit. This bit is set to 1 after a power-on reset. When
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Publication Release Date: September 1999
Revision A1