2-42
Workstation 4 and 4 LX Field Service Guide
WS4 Technical Overview
Customer Display/Mag Card Reader Port (COM3)
Multiplexer Operation
The primary component is U47, an 74HC125 Quad Buffer with 3-state outputs.
The device is composed of four buffers, the output of which is controlled by an
associated enable input.
A high on the
OE#
pin causes the associated buffer output to assume the High
Impedance or OFF state. A Low on the enable input passes the signal on the input
pin to the output pin.
The multiplexer operation is controlled by the WS4 API (UWS4.DLL Version
1.19 or later), and is part of the GR1.2 software platform. If an older version of the
WS4 API ends up on the AB28-I System Board, the multiplexer ceases to
function, and this breaks the MSR and Customer Display Interfaces it supports.
Following the release of the AB28-I System Board, this occurred all too often as
described below.
The WS4 with the AB28-I system board ships with the correct version of
UWS4.DLL and devices connected to COM3 function. The workstation is
connected to a 9700 server in order to download the POS application. The
application downloads, but a CAL scripting bug combined with out-of-date
platform files on the 9700 distribution media causes UWS4.DLL to be rolled back
to a version that does not support the multiplexer.
Several typical operations are described below. See Figure 2-24 for reference.
MSR Interface Active
By default, the WS4 API connects the MSR to COM3 at 9600 baud. This is done
by setting
MSR_IE#
from U15-2 low at U47-13 to pass
RXD_MSR
from the
reader at U47-12 to
MSR_REAR_RX
at U47-11.
MSR_REAR_RX
contains serial
data from a card swipe and is fed to U15-105.
Simultaneously, transmit data from U15 appears on
MSR_POLE_TX
at U46-1 and
is ORed with
MSR_OE#
at U46-2 to produce
TXD_MSR
at U46-3.
TXD_MSR
is
fed to the MSR connector CN10-5. This line is used is to send XOFF/XON
commands to the MSR during display updates as described below.
Reading and Writing to/from the Pole/Rear LCD Customer Display
COM3 simultaneously writes data to both Customer Display ports, the Rear and
pole connectors.
Just before the display update cycle occurs, the API sets the interface baud rate to
9600 and sends the MSR an XOFF command by setting
MSR_OE#
low at U46-1,
while placing the XOFF command on the
MSR_POLE_TX
line at U46-1. The
XOFF command essentially puts the MSR into a ‘stand-by’ mode where it is
capable of buffering a single card swipe. U8 is a TTL to RS232 level converter for
the RS232 based MSR.
Next, the API disconnects the MSR from COM3 by setting
MSR_IE#
high at
U47-3 to isolate
RXD_MSR
at U47-12 from
MSR_REAR_RX
at U47-11. The
transmit line to the MSR is disabled by setting
MSR_OE#
high at U46-2,
disabling
TXD_MSR
at U46-3. The MSR is now disconnected from COM3.
