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CPI/RS-232 Data Cable - CR1000X RS232 pinout

luisfgranada Jun 20, 2022 11:37 PM


According to the CR1000X's manual, the RS-232/CPI pinout is (I will write only RS232 relevant information):

Pin 1 - RS-232 Tx

Pin 2 - RS232 Rx

Pin 3 and 6 - 100 ohm Res Ground

Pin 7 - RS-232 CTS

Pin 8 - RS-232 DTR

According to Campbell's website https://www.campbellsci.com/31055, CPI/RS-232 data cable (PN 31055) pinout is:

Left is RJ45 CPI Bus (Datalogger - should match above information) - Right is RS-232 9 pin male cable

Pin 1 Tx - Pin 3 Tx

Pin 2 Rx - Pin 2 Rx

Pin 3 Ground - Pin 5 Ground

Pin 6 Ground - Pin 5 Ground

Pin 7 Sync B - Pin 4 DTR

Pin 8 Sync A - Pin 8 CTS

For me, most of it makes sense, Tx from datalogger goes to Tx from cable, same for Rx and ground. What I don't understand is why Pin 7 from datalogger (called RS-232 CTS in the CR1000X's manual) goes to Pin 4 DTR from cable when in an RS232 cable, CTS is Pin 8. Then Pin 8 from datalogger (DTR) goes to Pin 8 from cable which in RS232 should be CTS.

Shouldn't Pin 7 from datalogger (CTS) go to Pin 8 from cable (CTS) and Pin 8 from datalogger (DTR) go to pin 4 from cable (DTR)?


smile Jun 21, 2022 02:02 AM

there are 2 types of RS232 to CPI cables.

One to communicate with the PC and the other for the modems. (DCE or DTE)

It is necessary to do some inversions (nullmodem cable) to avoid that the input channels connect with the input channels of the other device or for the same reason output channels.

There is also another model https://www.campbellsci.co.uk/31056


luisfgranada Jun 23, 2022 09:37 AM

Hi smile,

We use 31055 to connect the datalogger to modems (DCE). So far, we have used cable 31055 by connecting it directly from the RS-232 port from Campbell CR1000X datalogger to port RS-232 from the modem (with flow control disabled) and it works. Now I'm testing a new modem for which flow control can't be disabled and I'm trying to understand why this cable is designed this way.

I don't understand why Pin 7 (called CTS in datalogger pinout and Sync B in cable 31055 pinout) goes to Pin 4 DTR and why Pin 8 (called DTR in datalogger pinout and Sync A in cable 31055 pinout) goes to Pin 8 CTS. If I connect this cable directly to a modem (DB9 female), this would mean that the signal CTS from the datalogger would connect to signal DTR from modem and that the signal DTR from the datalogger would connect to signal RTS from the modem.

smile Jun 25, 2022 02:03 PM

If I understand the matter, I believe that the jumpers between CTS and DTR are used to trick the modem into hardware flow control.


luisfgranada Jun 27, 2022 09:37 PM

Hi smile,

Just so you know, connecting RTS with CTS on the modem did the trick.

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