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.

qAfter receiving a character from the host

qEach time the printer is placed online

qAt the completion of a host-generated initialization cycle

Communication Interfaces 10-8

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Epson 8900 Series manual Data Signals, Data Strobe Signal, Acknowledge Signal