W921E840A Datasheet, PDF (15/58 Pages) Winbond – 4-BIT MICROCONTROLLER

W921E840A/W921C840
6.2.3 Working Register Area
The located area from 040H to 04FH is known as working register. The instruction MOV WRn, A or
MOV A, WRn can move the A accumulator data to the working register or move working register data
to the A accumulator directly within the 1 word / 1 machine cycle. The other direct instructions such
as MOV Mx, A or MOV A, Mx instruction are 2 words / 2 machine cycles. Therefore the working
register can save the program memory size in ROM and improve the control speed in µC application
circuit.
Only the WR0 to WR7 are available in the arithmetic and logic operation (I. e. only 040H to 047H can
be active). The instructions are as follows:
ADD A,
ADC A,
SUB A,
SBC A,
ANL A,
ORL A,
XRL A,
CMP A,
where x = 0 to 7.
WRx
WRx
WRx
WRx
WRx
WRx
WRx
WRx
6.3 Internal Oscillator Circuit
There are dual clocks in this chip, one high speed, the other low speed. The block diagram is shown
below:
f _TM0
TM0
f SYS1
MUX0'
f _SYS0
MUX0
SYSCCR.0
TM1
f TM1
MUX1
TM2
f TM2
MUX2
TM3
f TM3
MUX3
11-bit
Prescaler
5-bit
Prescaler
f SYS _{System Clock} f OSC
(1/4)
f1
f2
f SUB _{2-bit scaler}
(1/4)
SYSCCR.3
Mask
Option
OSCI
f H _{Crystal Type or}
RC Type
OSCO
Enable (SYSCCR.1)
f L 1-bit
scaler
(1/2)
XT
Crystal Type
XT
Enable (SYSCCR.2)
- 15 -
Publication Release Date: July 1999
Revision A3