Electronic – What DSUB9 to DSUB9 cable is this

cables

I'm sorry if this is the wrong use for stack exchange. I'm sure I will be notified by users if it is.

I have inherited a (female) DSUB9 to (female) DSUB9 cable from a very old project. The pinning perplexes me. What pinning is this? I mean, what is the name of this arrangement? I want to order at least one more. I could just deal with it and make an adapter for some female-to-male cable I have, but I want to understand.

EDIT: It's used to programmed a Cypress Semiconductor MCU CY90F543GSPFR-GE1

The cable is correct by the way, both pin 6 and 8 on one side go to pin 4 on the other. I figured it must be null-modem, but it does not match, as far as I can tell.

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Best Answer

It's close to a plain old null modem cable.

DB9 female according to RS-232:

  1. DCD (data carrier detect)
  2. Tx (transmit, pair with Rx)
  3. Rx (receive, pair with Tx)
  4. DTR (data terminal ready, pair with DSR)
  5. GND (signal ground)
  6. DSR (data set ready, pair with DTR)
  7. CTS (clear to send, pair with RTS)
  8. RTS (ready to send, pair with CTS)
  9. RI (ring indicator)

Everything in your pin list matches this except on a proper null modem, you are supposed to connect CTS with RTS rather than with DCD. So you appear to have some specialized, non-standard version. It's somewhat common in non-standard pinouts to give supply voltage on one pin, such as 1.

Edit: in case this was used for MCU programming over RS-232 bootloader, then it's quite likely that some of these pins are used for reset, reference voltages, mode select or similar. Older flash parts often required a high programming voltage > TTL levels at some pin.

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