¡ Semiconductor
MSM81C55-5RS/GS/JS
(1) Programming the Command/Status (C/S) Register
The contents of the command register can be written during an I/O cycle by addressing it
with an I/O address of xxxxx000. Bit assignments for the register are shown below:
7
6
5
4
3
2
1
0
TM2 TM1
IEB
IEA
PC2
PC1
PB
PA
Definition of PA0 - 7
Definition of PB0 - 7
0= Input
1= Output
00=ALT1
11=ALT2
01=ALT3
10=ALT4
See the port
control
Definition of PC0 - 5
assignment
table.
Port A Interrupt Enable
Port B Interrupt Enable
1 = Enabled
0 = Disabled
00 = NOP : Does not affect counter operations.
01 = STOP : Stops the timer if it is runnning.
NOP if the timer is not runnning.
Timer Command
Stops the timer when it reaches TC.
10 = STOP AFTER TC :
NOP if the timer is not running.
11 = START : If the timer is not running, loads the mode and
the count length, and immediately starts timer operation.
If the timer is running, loads a new mode and the count
length, and starts timer operation immediately after
TC is reached.
Port Control Assignment Table
Pin
PC0
PC1
PC2
PC3
PC4
PC5
ALT1
ALT2
ALT3
A INTR
ALT4
A INTR
A BF
Input port
Input port
Input port
Input port
Input port
Input port
Output port
Output port
Output port
Output port
Output port
Output port
A BF
A STB
A STB
B INTR
B BF
Output port
Output port
Output port
B STB
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