Avery Berkel CX20 SERIES, Service Manual

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23 — RS232 Interface PCB (CX20 W)
23–4 CX20/CX30/CX34 Service Manual
An RS232 serial interface transmits data .at 2400 Baud to the ULMA UL200
Series of machines.
23.2 Circuit Description
The RS232 interface PCB provides an RS232 serial channel by automatically
multiplexing the DCU channel.
23.2.1 RS232 interface
The DCU has a hard–wire link inside the D–type shell. The main PCB drives
one end of the link with a multiplexed scan pulse and reads the other via a
buffer to establish when the DCU is connected.
The ’switched’ DCU channel on the RS232 interface PCB also checks for the
presence of this scan pulse to disable the RS232 channel when the DCU is
connected. When present, the scan pulse is used to trigger a re–triggerable
monostable (IC3). This produces a high signal that then disables tri–state
buffers (IC4 A–B) disconnecting the RS232 Rxd and RTS signals.
The default condition when no external device is connected to the DCU port is
such that all four RS232 signals are enabled. These signals are opto–isolated
using 6N139 opto–couplers and then converted to RS232 levels via a 75154
(IC10) and a 75150 (IC11).
23.2.2 Wrapper control signal interface
The RS232 interface PCB has two versions of hardware handshaking control to
make it more flexible for future alternative applications. Both control interface
versions use the same control lines and are, therefore, mutually exclusive.
Control interface version 1 is implemented as one standard RS232 RTS output
signal and one standard CTS input signal if at some stage in the future they are
required. For this version 0R resistors R40, R42 and R43 are fitted and R39,
R41 and R44 omitted from the RS232 interface PCB.
Control interface version 2 is implemented specifically for the ULMA machine
and consists of one input signal (Wrapper Ready) and one output signal (Scale
In Control). Voltage levels 0V and +24V are supplied from the ULMA wrapping
machine. For this version 0R resistors R39, R41 and R44 are fitted and R40,
R42 and R43 omitted from the RS232 interface PCB.
NOTE: The standard RS232 interface PCB assembly will be built to
version 2, namely ”Wrapper Ready” and ”Scale In Control” signals.
23.2.3 Wrapper ready signal (control interface version 2 only)
This signal is an input to the scale and is used by the scale’s software to
determine when the wrapper is switched on and setup in the correct operating
mode. The scale’s software will detect 0V on DUART CTS channel B input pin
when the wrapper is ready for use.