Nibble Mode - Canon BJC-55 Service Manual

Part 4: Technical Reference

2.1.2 Nibble mode

In nibble mode, the printer transfers data twice to the host computer in 4-bit units.
The data is transferred with the PtrClk signal and HostBusy signal handshakes.
After the printer negotiates with the host computer and enters the nibble mode, the
printer confirms that the HostBusy signal is low, outputs a PtrClk signal with a nibble
setting on the lower bits and lowers the PtrClk signal. After the host computer
receives the lower bit data with the nibble mode, it raises the HostBusy signal. This
signals the printer that the host computer has read the nibble data. Next, after the
printer confirms that the HostBusy signal is low for a second time, it outputs the
upper nibble bits and lowers the PtrClk signals.
When the host computer raises the HostBusy signal, the handshake is completed. 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.
Host Busy
PtrClk
Data Avail
Xflag
AckDataReq
Ptr Busy
Tp
Figure 4-7 Interface Timing (Nibble Mode)
bit0 bit4
bit1 bit5
bit2 bit6
bit3 bit7
Tp
4-10
BJC-50