AN00011.TXT Advanced Communication Board Developer's Toolkit 1995 ---------------------------------------------------------------------- ---------------------------------------------------------------------- Subject: Constructing a Loop-Back Plug for Testing. Loop-back plugs are diagnostic tools that do just as their name suggests, they "loop-back" signals from one place on the external connector to another. They are required when an "external loop-back test" is performed. In their simplest form only the Transmit Data (TD) and Receive Data signal are "looped" together. This is accomplished by taking a wire with the correct gender pin attached and connecting on the external connector signals TD to RD. For example the RS-232 data loop-back would be pin 2 (TD) to pin 3 (RD). To perform more through diagnostic testing more signals can be added to the loop-back. The following table diagrams the typical RS-232 Diagnostic loop-back. When constructing a loop-back for testing purposes, first decide which signals need to be tested. In most cases, it will be necessary to loop-back the Transmit and Receive signals. When testing a synchronous protocol such as HDLC or SDLC, clocks signals will be needed. Most ACB adapters have three clock signals, and some have only two clock signals. When making the loop-back plug, remember if using a differential interface, such as RS-422, EIA-530, MIL-188/114 or V.35, connect positive signals to positive signals (i.e. TX+ to RX+ and TX- to RX-). The following is a listing of common loop-back wiring diagrams. If loop-back configuration needed is not listed, or if there are any questions concerning the listed examples, please contact technical support at the numbers listed in the README.TXT file located in the root directory of this disk. Most asynchronous transmit, receive, and terminal emulation examples require the following connections when interfacing to another asynchronous device: RS-232 RS-422 ACB-II,III DTE DCE ACB-II DTE/DCE ---------- ----- ----- ---------- ---------- TD(2) ------ RD(3) --- RD(2) TD+ (24) ------ RD+ RD(3) ------ TD(2) --- TD(3) TD- (25) ------ RD- GND(7) ------ GND(7) --- GND(7) RD+ (12) ------ TD+ RD- (13) ------ TD- RS-530 ACB-IV DTE DCE -------- --------- -------- TD+ (14) --- RD+ (16) --- RD+ (14) TD- (2) --- RD- (3) --- RD- (2) RD+ (16) --- TD+ (14) --- TD+ (16) RD- (3) --- TD- (2) --- TD- (3) Most asynchronous point-to-point examples require the following connections: ACB-II,III (RS-232) ACB-II (RS-422) ------------------------ ------------------------- TD(2) ---------- RD(3) TD+ (24) ----- RD+ (12) RD(3) ---------- TD(2) TD- (25) ----- RD- (13) RTS(4) ---------- CTS(5) RD+ (12) ----- TD+ (24) RD- (13) ----- TD- (25) RTS+ (22) ----- CTS+ (10) RTS- (23) ----- CTS- (11) ACB-IV (RS-530) CTS+ (10) ----- RTS+ (22) ------------------------ CTS- (11) ----- RTS- (23) TD+ (14) ----- RD+ (16) TD- (2) ----- RD- (3) RD+ (16) ----- TD+ (14) RD- (3) ----- TD- (2) RTS+ (19) ----- CTS+ (13) RTS- (4) ----- CTS- (5) CTS+ (13) ----- RTS+ (19) CTS- (5) ----- RTS- (4) Most HDLC/SDLC procedures require the following point to point connections: RS-232 ACB-II ACB-II | ACB-III ACB-III TRANSMITTER RECEIVER | TRANSMITTER RECEIVER --------- ---------- | --------- ---------- TD(2) ---------- RD(3) | TD(2) ---------- RD(3) RD(3) ---------- TD(2) | RD(3) ---------- TD(2) GND(7) ---------- GND(7) | GND(7) ---------- GND(7) RXC(6) ---------- TXC(20) | RXC(17) --------- TXC(15) TXC(20) --------- RXC(6) | TXC(15) --------- RXC(17) RS-422(530) ACB-II ACB-II | ACB-IV ACB-IV TRANSMITTER RECEIVER | TRANSMITTER RECEIVER --------- ---------- | --------- ---------- TD+ (24) ------- RD+ (12) | TD+ (14) ------- RD+ (16) TD- (25) ------- RD- (13) | TD- (2) ------- RD- (3) RD+ (13) ------- TD+ (24) | RD+ (16) ------- TD+ (14) RD- (12) ------- TD- (25) | RD- (3) ------- TD- (2) RXC+(8) ------- TXC+(20) | RXC+(9) ------- TXC+(12) RXC-(9) ------- TXC-(21) | RXC-(17) ------- TXC-(15) TXC+(20) ------- RXC+(8) | TXC+(12) ------- RXC+(9) TXC-(21) ------- RXC-(9) | TXC-(15) ------- RXC-(17) Most full duplex examples require the following loop-back connector: ACB-III (RS-232) ACB-IV (RS-530) ----------------------- ----------------------- TD(2) ------- RD(3) TD+ (14) ------- RD+(16) RXC(17) ------- TXC(15) TD- (2) ------- RD-(3) RXC+(9) ------- TXC+(12) RXC-(17) ------- TXC-(15) Most examples and test programs require the following loop-back connections: TD (2) ------ RD (3) RTS (4) ------ CTS (5) RTS (4) ------ RI (22) * (Ring Indicator is not available on most DTR (20) ------ DCD (8) ACB Boards) DTR (20) ------ DSR (6) TXC (15) ------ RXC (17) * * Often the TSET signal are used in place of the TXC signals. In this case substitute pins 24 for TSET. When working with RS-422 or RS-530 both sets of differential signals must be looped back. The following example illustrates the RS-530 loop-back. TD- (2) ------ RD- (3) TD+ (14) ------ RD+ (16) RTS- (4) ------ CTS- (5) RTS+ (19) ------ CTS+ (13) DTR- (20) ------ DCD- (8) DTR+ (23) ------ DCD+ (10) DTR- (20) ------ DSR- (6) DTR+ (23) ------ DSR+ (22) TXC- (15) ------ RXC- (17) * TXC+ (12) ------ RXC+ (9) * * Often the TSET signals are used in place of the TXC signals. In this case substitute pins 11 & 24 for TSET +/-. To run all Asynchronous Loop-back test samples, only a simple data loop-back (TD-RD) is needed. To run the synchronous loop-back test, the loop-back must include data and clock signals (TD-RD and TXC-RXC).