Canon BJC-55 Service Manual page 68

Part 2: Product Specifications
ECP MODE
STROBE [Input] (Host Clk):
STROBE signal handshakes with the BUSY signal (Periph Ack) to transmit data from
the computer to the printer during the forward phase. When STROBE signal is low,
it indicates that data has been sent to data bus. Reverse phase is always high.
DATA 1~8 [Input]:
When the host computer outputs data during the forward phase, DATA signal is
input signal. When the printer outputs data to the host computer during the reverse
phase, DATA signal is output signal.
INIT [Input] (Reverse Req):
INIT signal is set to low to perform a recovery process of the data sent from the host
computer during the forward phase. INIT signal responds to the low PE signal and becomes
high. INIT signal is lowered when the forward phase idle is switched to the reverse phase.
When the reverse phase is switched to forward phase, INIT signal is raised to high.
AUTO FEED XT [Input] (Host Busy):
During the forward phase, the AUTO FEED XT signal on data bus indicates whether
the information is in a data or command form.
Low: Command form
High: Data form
SELECT IN [Input] (1284 Active):
SELECT IN signal is high at the beginning of negotiation and remains high during
the ECP mode. This indicates that the printer is operating under bidirectional mode.
After completing the ECP mode, SELECT IN signal is low.
ACKNLG [Output]:
The ACKNLG signal is always high during the forward phase. During the reverse
phase, ACKNLG signal is low to indicate data has been outputted from the host
computer to the data bus. ACKNLG signal responds high to the host computer's
AUTO FEED XT signal high signal.
P.E. [Output] (AckReverse):
PE signal is always high during the forward phase and it is always low during the
reverse phase. PE signal is lowered in response to the host computer's low INIT
signal to confirm the request to transfer from the forward phase to the reverse phase.
SELECT [Output] (X flag):
SELECT signal is always high.
ERROR [Output] (Periph Req):
If there is still data to be transferred in the host computer, a low ERROR signal is
released to request reverse phase.
BUSY [Output] (PeriphAck):
During the forward phase, BUSY signal is low if the computer can send data. Once
the data has been outputted BUSY signal becomes high. During the reverse phase,
the form of data sent from the printer to the data bus is shown as follows:
Low: Command form
High: Data form
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BJC-50