Service manual

Circuit Description

3-23

3-4 HOST INTERFACE:

Referred to IEEE 1284 standard.

3-4-1. Host Interface

PARALLEL PORT INTERFACE PART ARM946ES has the Parallel Port Interface Part that enables Parallel

Interface with PC. This part is connected to PC through Centronics connector. It generates major control

signals that are used to actuate parallel 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 to transmit data to the printer. ECP mode is an improved pro-

tocol for the communication between PC and peripherals such as printer and scanner, and it provides

high speed two-way data communication. ECP mode provides two cycles in the two-way data transmis-

sion; data cycle and command cycle. The command cycle has two formats; Run-Length Count and Chan-

nel Addressing. RLE (Run-Length Count) has high compression rate (64x) and it allows real-time data

compression that it 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 struc-

ture. 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 signals 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 sys-

tem control signal and overall system from PC are all processed through this part.

PPD( 7: 0)

nSTROBE

BUSY

nAC

DATA