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Communication Interfaces 10-11
The following figure shows the timing sequence for host-to-printer
character-transfer operations. The table on the following page lists
the timing requirements for the operation.
The reference points, a through h in the preceding figure, are keyed to
the table on the following page and to the following character-transfer
sequence.
1. The host writes a character to the parallel data lines (a). (The
data stabilization time, a-b, must elapse before the transfer cycle
can begin and the minimum data hold time, b-c, must elapse
before the host can write a subsequent character.)
2. After writing the character to the interface, the host monitors the
BUSY line to ensure that the printer is ready to receive a character.
If BUSY is inactive, and the required data stabilization time has
elapsed, the host activates STROBE- to begin the transfer cycle.
The leading edge of STROBE- (b) clocks the character into the
printer receive buffer and activates BUSY.
▲
▲
▲
▲
▲
▲
▲
BUSY
DATA1-8
STROBE-
ACK-
reference
line
valid data valid data
parallel data timing sequence
a
b
c
d
e
f
g
h