USER MANUAL

Chapter 7

The Parallel Port

7–15

You can tie the strobe lines high because message zero is ignored. Keep all

data lines at zero, until you want to trigger a message. The last message is

only triggered once --no matter how long the data lines stay in their state

(DL20 rejects unchanging data). To trigger the same message twice in a row,

the message must be triggered, the data lines must return to a zero state, the

message can then be retriggered. The following diagram shows how

message 7 could be triggered once and message 12 triggered twice using the

connections shown in Figure 7.4.

t3t2t1t0 t9t8t7t6t5t4

MS0

MSI

t6: A zero is presented to the DL20. Twelve cannot be presented

here, because the DL20 will not queue the same message twice

in a row, as long as MS0 and MS1 remains ON. In this example,

MS0 and MS1 are always ON.

t7: The data lines change state, from zero to twelve.

t8: The message trigger twelve is queued up.

t9: The last message has been triggered, the data lines may remain

in their previous state or they may change back to zero.

t0: The value on the data lines is zero, the DL20 ignores this

value because there is no message zero.

t1: The data lines change state, from zero to seven.

t2: The message trigger seven is queued up.

t3: The data lines change state, from seven to twelve.

t4: The message trigger twelve is queued up.

t5: The data lines change state, from twelve to zero.