HD404849 Datasheet, PDF (63/125 Pages) Hitachi Semiconductor – 4-Bit Single-Chip Microcomputer

HD404849 Series
Timer B is initialized by writing to timer write register B (TWBL: $00A, TWBU: $00B). In this case,
the lower digit (TWBL) must be written to first, but writing only to the lower digit does not change the
timer B value. Timer B is initialized to the value in timer write register B at the same time the upper
digit (TWBU) is written to. When timer write register B is written to again and if the lower digit value
needs no change, writing only to the upper digit initializes timer B.
Timer write register B (lower digit) (TWBL: $00A)
Bit
Initial value
Read/Write
Bit name
3
0
W
TWBL3
2
0
W
TWBL2
1
0
W
TWBL1
0
0
W
TWBL0
Figure 46 Timer Write Register B Lower Digit (TWBL)
Timer write register B (upper digit) (TWBU: $00B)
Bit
Initial value
Read/Write
Bit name
3
2
1
0
Undefined Undefined Undefined Undefined
W
W
W
W
TWBU3 TWBU2 TWBU1 TWBU0
Figure 47 Timer Write Register B Upper Digit (TWBU)
• Timer read register B (TRBL: $00A, TRBU: $00B): Read-only register consisting of a lower digit
(TRBL) and upper digit (TRBU) that holds the count of the timer B upper digit. See figures 48 and 49.
The upper digit (TRBU) must be read first. At this time, the count of the timer B upper digit is
obtained, and the count of the timer B lower digit is latched to the lower digit (TRBL). After this, by
reading TRBL, the count of timer B when TRBU was read can be obtained.
Timer read register B (lower digit) (TRBL: $00A)
Bit
Initial value
Read/Write
Bit name
3
2
1
0
Undefined Undefined Undefined Undefined
R
R
R
R
TRBL3 TRBL2 TRBL1 TRBL0
Figure 48 Timer Read Register B Lower Digit (TRBL)
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