4-97

Mode 2

Operation of this mode is the same as mode 1, except the

outputs will change for one clock period only and then return

to the condition of TXO high and TXO low, and the counter is

reloaded

Mode 3

After the jam register is loaded with the required value, the

gate edge will initiate this mode. TXO will be set high, and

TXO will be set low. The clock will decrement the counter.

When zero is reached, TXO will go low and TXO will be high,

and the interrupt output will be set low. The counter is retrig-

gerable: While the counter is decrementing, a gate edge or

write to the control register with the jam-enable bit high, will

load the counter with the jam register value and restart the

one-shot operation.

MODE

CONTROL REGISTER

GATE CONTROL

2

Timeout Strobe

Selectable High or Low

Level Enables Operation

XXXXX0 1 0

BUS 7

BUS 0

FIGURE 2. TIMEOUT STROBE (MODE 2) TIMING WAVEFORMS

NOTE: Write to control register with mode selects = 0

COUNTER VALUE

CLOCK

WR CONTROL

REGISTER

GATE

TXO

INT

1

2

3

3

LOAD COUNT = 3

0

1

2

3

0

1

2

3

3

0

1

2

3

SEE NOTE

MODE

CONTROL REGISTER

GATE CONTROL

3

Gate Controlled One-Shot

Selectable Positive or

Negative Going Edge

Initiates Operation

0 XXXX0 1 1

BUS 7

BUS 0

FIGURE 3. GATE CONTROLLED ONE-SHOT (MODE 3) TIMING WAVEFORMS

COUNTER VALUE

CLOCK

WR CONTROL

REGISTER

GATE

TXO

INT

LOAD COUNT = 3

2

3

3

0

1

2

3

3

1

2

3

0

1

2

3

CDP1878C