Xerox M20 - WorkCentre B/W Laser, Service Manual

Page: 255 / 314

December 2006
6-49 WorkCentre M20, 4118, FaxCentre 2218 Family
GP 14, GP 15
General Procedures and Information
Figure 3 Block Diagram of CIP4
GP 15 Host Interface
Purpose
To give information about the machines interfaces:
• Host Interface
• USB Interface
Referred to IEEE 1284 standard.
NOTE: If necessary, refer to GP 20 for the acronym list and cross reference lists of more com-
monly recognised part names.
Host Interface
PARALLEL PORT INTERFACE PART ARM946ES (M20F) or ARM920T (4118) has the Paral-
lel Port Interface Part that enables Parallel Interface with a PC. This part is connected to a PC
through a Centronics connector. It generates major control signals that are used to actuate par-
allel communication. It is comprised of /ERROR, PE, BUSY, /ACK, SLCT, /INIT, /SLCTIN, /
AUTOFD and /STB. This part and the PC data transmission method support the method
specified in IEEE P1283 Parallel Port Standard (http://www.fapo.com/ieee1284.html). In other
words, it supports both compatibility mode (basic print data transmitting method), the nibble
mode (4bit data; supports data uploading to PC) and ECP (enhanced capabilities port: 8bits
data - high speed two-way data transmission with PC).
Compatibility mode is generally referred to as the Centronics mode and this is the protocol
used by most PC’s to transmit data to a printer. ECP mode is an improved protocol for the com-
munication between a PC and peripherals such as a printer and a scanner, and it provides high
speed two-way data communication. ECP mode provides two cycles in the two-way data trans-
mission; data cycle and command cycle. The command cycle has two formats; Run-Length
Count and Channel Addressing. RLE (Run-Length Count) has high compression rate (64x)
and it allows real-time data compression that is useful for the printer and scanner that need to
transmit large raster image that has a series of same data. Channel Addressing was designed
to address multiple devices with single structure. For example, like this system, when the fax/
printer/scanner have one structure, the parallel port can be used for other purposes while the
printer image is being processed. This system uses RLE for high speed data transmission.
PC control signal and data send/receive tasks such as PC data printing, high speed uploading
of scanned data to PC, upload/download of the fax data to send or receive and monitoring the
system control signal and overall system from PC are all processed through this part.