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Communication Interfaces 10-8
Data Signals
Character transfers from the host to the receiver consist of 8-bit data
bytes (DATAl through DATA8) traveling in parallel over the eight
data lines. DATAl is the least significant bit and DATA8 is the most
significant bit. If a 7-bit character set has been selected, the DATA8
line remains low for all data transfer operations.
Data Strobe Signal
The data strobe (STROBE-) is a host-generated pulse that clocks
data into the printer receive buffer. After writing data to the parallel
interface data lines (DATAl through DATA8), the host monitors the
busy line, and if BUSY is not active (low), the host places a strobe
pulse on the interface. This strobe pulse must not occur before the
data has had time to stabilize on the data lines (approximately 0.5
microseconds). The leading (negative-going) edge of STROBE-
clocks the data into the printer receive buffer and activates BUSY.
Acknowledge Signal
The acknowledge (ACK-) signal from the printer indicates to the
host that the printer has received the last character sent and is ready
to accept another character. Unless the printer is busy, as described
in the following paragraph, the printer activates ACK- (sets it low)
under any of the following conditions.
q After receiving a character from the host
q Each time the printer is placed online
q At the completion of a host-generated initialization cycle