Firmware; Interface; Nibble Mode - Canon BJC-8500 Service Manual

Part 4: Technical Reference

2. FIRMWARE

2.1 Interface

This printer supports a nibble mode and ECP mode that are both compliant with bi-
directional Centronics interface standard (IEEE 1284).

2.1.1 Nibble mode

In nibble mode, the printer transfers 8 bits of data to the host computer divided into
two 4-bit blocks..
After the printer negotiates with the host computer, the printer lowers the DataAvail
signal.
After confirming the falling edge of the HostBusy signal, the printer sets 8-bit data,
and lowers the PtrClk signal to output the lower 4 bits of data onto the control signal
line.
The host computer receives the data after the falling edge of the PtrClk signal, and
raises the HostBusy and PtrClk signals.
After the printer confirms that the HostBusy signal is low for a second time, it outputs
the upper 4 bits of data onto the control signal line.
When the host computer raises the HostBusy signal, if there is no data to be sent to
the host computer, the DataAvail signal becomes high and the printer stands by for
the next data transfer.
1284Active
High
AckDataReq
HostBusy
HostClk
PtrClk
PtrBusy
Status maintained.
(Busy)
DataAvail Data Available
Xflag Nibble Mode Support
Bit2
35msMax
500msMax
Bit3
Bit0
Bit1
Figure 4-8 Interface Timing (Nibble Mode)
4-8
Bit6
35msMax
35msMax
Bit7
Bit4
Bit5
BJC-8500