MSM82C54-2RS Просмотр технического описания (PDF) - Oki Electric Industry

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MSM82C54-2RS

CMOS PROGRAMMABLE INTERVAL TIMER

Oki Electric Industry 

¡ Semiconductor

MSM82C54-2RS/GS/JS

(3) Read Back Command Operation

Use of the read back command enables the user to check the count value, program mode,

output pin state and null count flag of the selected counter.

The command is written in the control word register, and the format is as shown below. For

this command, the counter selection occurs according to bits D3, D2 and D1.

D7

D6

D5

D4

D3

D2

D1

D0

1

1 COUNT STATUS CNT2 CNT1 CNT0

0

(CS=0, A0, A1=1, RD=1, WR=0)

D5: 0 = Selected counter latch operation

D4: 0 = Selected counter status latch operation

D3: 1 = Counter #2 selection

D2: 1 = Counter #1 selection

D1: 1 = Counter #0 selection

D0: 0 = Fixed

It is possible to latch multiple counters by using the read back command. Latching of a read

counter is automatically canceled but other counters are kept latched. If multiple read back

commands are written for the same counter, commands other than the first one are ignored.

It is also possible to latch the status information of each counter by using the read back

command. The status of a certain counter is read when the counter is read. The counter

status format is as follows:

Bits D5 to D0 indicate the mode programmed by the most recently written control word.

Bit D7 indicates the status of the output pin.

Use of this bit makes it possible to monitor the counter output, so the corresponding

hardware may be omitted.

D7

D6

D5

D4

D3

D2

D1

D0

OUTPUT

NULL

COUNT

RL1

RL0

M2

M1

M0

BCD

D7: 1 = Output pin status is 1.

0 = Output pin status is 0.

D6: 1 = Null count

0 = Count value reading is effective

D5 - D0: Programmed mode of counter

(See the control word format.)

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