PCM-2 Manual.pdf - Voss Associates

Special Functions
The RS-485 transmitter and Receiver chip (A102) is protected by two spark gaps
GT-1 and GT-2 and surge suppressor CR1-CR4. High voltage on either of the
RS-485 communication lines initially are clamped by CR1 to CR4 and current
limited by R12 & R13. GT-1 and GT-2 provide protection after voltage
breakdown has occurred. A grounding lug is provided on the chassis of units that
use this board. This lug should be connected to a good earth ground by a 14
gauge copper wire for best operation of the protection circuit.
If this board is to be used with an unregulated supply, as in the PCM-2, regulator
A103 and C1 may be added and jumper JP-l cut.
The RS-485 communication protocol defines only voltage levels of transmission
and electrical characteristic of the transmitters and receivers. The character
protocol, baud rate, number character bits, stop bits, and parity must be selected
to match for both transmitters and receivers.
RS-232 to RS-485 Interface Parts List
The following table lists the electronic items incorporated in the RS-232 to RS-485
Interface Board and should contain any part necessary for normal electronic
repair. Unless otherwise specified callouts of manufacturers and manufacturers'
part numbers are to be considered typical examples only and not restrictions
against using equivalent parts with the same operating characteristics. When
ordering parts from Eberline, specify model number, serial number, reference
designation, value and Eberline part number, or a word description if the part has
no reference designation. Eberline will automatically substitute equivalent parts
when the one called out by the manufacturers' part number is not available.
RS-232 to RS-485 Interface, YP11451000
Ref. Desig. Part Name Description
Manufacturer
Part Number
Eberline
Part Number
A100 I.C. RS-232 to TTL converter Maxim MAX233CPP ICXXMAX233
AlOI I.e. Dual comparator T.I. TLC372CP
ICACA372
A102 I.C. RS-485 Transceiver National DS3695N ICXXAS3695
A103 I.C. Voltage regulator, 5V National LP2950CZ-5.0 ICAVA2950C
CI Capacitor 0.047 p,F, 50Y, 20% Kemet
C32lC473M5U5CA
CPCE473P4N
C2 Capacitor 33 ~(F, lOY, 10% Sprague 199D CPXX12
12-2
PCM2.MAN/ Rev A/April 1995