Camiacs Model V document V0.3 update

drlegendre . drlegendre at
Thu Jan 1 23:17:08 CST 2015

Camiacs RS-232 / CL converter Model V document - Updated, with corrections.

Your comments / additions / etc are of course requested.
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Camiacs Model V RS-232 - Current Loop converter info-sheet - Ver. 0.3 - 01-JAN-2014
(c) 2014 legendre at - This document may be freely redistributed under the terms of the current GNU/GPL license. 

Circuit board "RS232/CL MODEL 5 CAM 25-116A"

I. External ports

	A. RS-232 Port (DB25-F) pinout information:

	2 - TXD
	3 - RXD
	5 - CTS *
	6 - DSR *
	7 - GND
	8 - DCD  / RLSD *
	1, 4, 9-25 - N/C

	(* = Manually set active / inactive with internal jumper. Default = active. See end notes for further information.)

	B. Current Loop Port (DB25-F) pinout information:

	1 - Rx+
	2 - Rx-
	3 - Tx+
	4 - Tx-

	C. AC mains power

	Voltage - 117V AC via IEC connector on rear panel
	Red LED power indicator on front panel
	Utility sockets - Two (2) on rear panel, fused.
	Power consumption - 5W (40mA) average, not including utility socket load

II. Internal features

	A. Fuse information:

	Buss MDX 5A / 250V - Bottom of PCB

	B. LED information:

	LED1 - Tx loop activity
	LED2 - Rx loop activity

	Note: Apparent LED brightness is proportional to magnitude of loop current & data rate. 
	Higher current level and/or lower data rate = higher relative brightness. 

	B. Loop current power supplies (24V / 55mA short-circuit):

	Jumper set T1-T9 - Tx loop power
	T2-T3, T4-T5, T6-T7 = Tx Active (Default)
	T1-T2, T3-T4, T5-T6 = Tx Passive

	Jumper set R1-R9 - Rx loop power 
	R2-R3, R4-R5, R6-R7 = Rx Active
	R1-R2, R3-R4, R7-R8 = Rx Passive (Default)

III. Additional Notes

1) While this converter is intended for 20mA current loop operation, the DC power supply is configured for 24V DC @ 55mA short-circuit. For short runs, use an appropraite current-limiting resistor in the loop(s) to attenuate current to 20mA nominal. 750R @ 1/2W is suggested for short runs; 470R - 1K should be acceptable.  

2) Being that the current loop protocol does not support any form of hardware flow control, as does the RS-232 protocol, the various jumper settings for the CTS, DSR and DCD / RLSD lines are only present to satisfy the requirements of the RS-232 device. They have no bearing on the activity or status of the current loop Rx / Tx lines, where only software flow control (XON / XOFF) may be implemented.

3) A simple loopback test can be made as follows: On the current loop port, connect Pins 1&3 with a 750R 1/2W, and Pins 3&4 with a second 750R 1/2W. Any data sent to the RS-232 port will be echoed back to the sending device. When performing a loopback test, be sure to de-select "Local echo" on the RS-232 side, lest there be any confusion (false positive). However, it is allowable and may be necessary to select "Add linefeed" on the RS-232 side. 

4) The 6-pos. jumper header near the edge of the board, adjacent to D1 and D2, is for spare jumper storage only. This header is not connected to the circuitry. 

5) IC 1 is the Tx opto-coupler, IC 2 is the Rx opto-coupler.

6) There is a 7-pos. jumper header, fitted with two jumpers, on the edge of the board adjacent to IC 5. The purpose of this header has not presently been discovered, but it appears to select which outputs from the MC1489A are delivered to the rest of the circuitry. The default settings are 2-3 and 6-7, with pin 1 being closest to the rear of the chassis. 

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