Canon MultiPASS C50 Service Manual page 253

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 ( ).
The facsimile sets the low-order nibble of the byte (0 to 3 bits) to four lines: nDataAvail, Xflag,
AckDataReq, and PtrBusy. (These lines are the reverse channel data lines.)( ).
The facsimile sets PtrClk to low ( ), 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 ( ).
The host computer sets HostBusy to low to receive the data (4 to 7 bits) ( ).
4 to 7 bits data transfer is carried out as same as 0 to 3 bits transfer and 1 bite transfer completes ( ' ~ ').
If the next byte can be transferred, the facsimile sets nDataAvail to low ( ), and PtrClk to High to
responds to host's receipt ( ').
AckDataReq
P
(PError)
HostBusy
H
(nAutoFd)
PtrClk
P
(nAck)
PtrBusy
P
(Busy)
nDataAvail
P
(nFault)
Xflag
P
(Select)
P : Peripheral (Facsimile)
H : Host
Figure 2-6 Nibble Mode Facsimile to Host Data Transfer
Some types of host computers use a mode other than the Bi-Centronics interface Nibble
mode as default. In this case, the host computer must be set to Nibble mode. Check the
host computer specifications and change the print mode if necessary. The Nibble mode
NOTE is specified in the IEEE-P1284 standard, but it may be called differently STD, Uni-
Direction, Compatible, AT, etc. For some computers.
Data bit 2
Data bit 3
Data bit 0
Data bit 1
1 2 3 4 5 6
Data Transfer Phase
2-13
Chapter 2: Technical Reference
Data bit 6
Data bit 7
Data bit 4
Data bit 5
' ' ' '
2 3 4 7 5