Canon MultiPASS C5000 Service Manual page 210

b-2) Data transfer from the facsimile to the host computer In Nibble mode
Data is transferred by the following steps.
The host computer sets HostBusy to low to indicate that it is ready to receive data (0).
The facsimile sets the low-order nibble of the byte (0 to 3 bits) to four lines: nDataAvai1,
Xflag, AckDataReq, and PtrBusy. (These lines are the reverse channel data lines.)(Q).
The facsimile sets PtrClk to low (01, and the host computer receives data (0 to 3 bits).
The host computer sets HostBusy to high to notify the facsimile that the computer has
received data (@).
The facsimile sets PtrClk to high to end the data (0 to 3 bits) transfer (6).
The host computer sets HostBusy to low to receive the data (4 to '7 bits) (8).
4 to 7 bits data transfer is carried out as same as 0 to 3 bits transfer and 1 bite transfer
If the next byte can be transferred, the facsimile sets nDataAvail to low (an), and PtrClk to
High to responds to host's receipt (0').
PtrClk
P
Figure 2-6 Nibble Mode Facsimile to Host Data Transfer
Some types of host computers USC a mode other than the Bi-Centronics
set to Nibble mode. Check the bost computer specifications and change the
NOTE print mode if necessnry. Tile Nibble mode is specified in the IEEE-P1284
standard, but it may be called difliewntly STD, IJni-Direction, Compatible,
AT, etc. For some computers.
Chapter 2: Technical Reference
Data Transfer Phase
2-13