Kellan's proposal for a RS-232 serial wiring standard for sub-miniature-D-shell-to-8P8C-jack adapters: RYSC

I propose that all existing DB9 and DB25 RS-232 connections can be fitted with DB9-to-RJ45 or DB25-to-RJ45 jack adapters. This has the potential to obviate the existing maelstrom of serial cables, adapters and null modems that prevails; resulting in a universal physical connector for RS-232 with a single pinout... the RYSC 8P8C. I'll be calling these DB9-to-RJ45 or DB25-to-RJ45 adapters 'RYSC adapters' when configured as described herein.

The Reduced Yost Serial Connection (RYSC) standard described below pares down device-to-device RS-232 interconnects to the three signal connections required for duplex RS-232 communication: Transmit, Receive, and Signal Ground.

The remaining signals comprising RS-232 connections are the 'flow control' signals, specifically, 'hardware flow control signals'. These signals are nominally used to regulate the flow of data between the DCE and DTE, preventing buffer overflows among other things. Hardware Flow Control is often not required, utilized, or implemented at the application level.

The hardware flow control pins (RTS, CTS, DSR, and DTR) are interconnected within each RYSC adapter so that each device supplies its own flow control signaling, implementing flow control loopback within each adapter. Meanwhile, the Transmit, Receive, and Signal Ground lines are exposed via the 8P8C jack, allowing minimal 'three-wire serial connections' to be utilized even in applications nominally requiring hardware flow control between devices.

The five concepts of RYSC adapters

All DB9 and DB25 RS-232 ports are to have sub-miniature-D-shell-to-8P8C adapters, wired to the RYSC standard, permanently affixed.
Both pin 4 and pin 5 of the 8P8C side of the RYSC adapter must be connected to Signal Ground on the sub-miniature-D-shell side. - Signal ground is carried on DB9 pin 5, and DB25 pin 7.
On a DB9 DTE RYSC adapter, Black goes into pin 2 (Tx) and Yellow goes into pin 3 (Rx).
- My mnemonic is "The DB9 DTE serial port on my Terminal Transmits into the inky Blackness of the Internet, too [Two]."
- For DCE, reverse Tx/Rx assignment.
- For DB25 reverse Tx/Rx assignment (possibly a second reversal).
For self-handshaking Flow Control, 'strap' (bond/jumper/connect) the RTS/CTS and DSR/DTR signal line pairs within the adapter shell:
- On a DB9: strap pins 4 and 6 (RTS and CTS), also, strap pins 7 and 8 (DSR and DTR).
- On a DB25: strap pins 4 and 5 (RTS and CTS), also, strap pins 6 and 20 (DSR and DTR).
Straight-through) RYSC serial cables are 8P8C UTP 'rollover cables', wired 'with a twist', meaning that the pinouts of the opposite ends of the cable are mirror-images of each other. Any cable pinned as such will function as a 'straight serial cable' when used with RYSC adapters.
- RYSC Null-Modem cables are simply run-of-the-mill 8P8C UTP patch cables. Note, this means that any two devices requiring a Null-Modem to communicate (be they DB9 or DB25, male or female) can be connected by plugging a run-of-the-mill Ethernet patch cable into their RYSC adapters.
- 8P8C straight-to-rollover adapters (available commercially or manufactured in the field) act as universal RYSC Null-Modems, attaching to common Ethernet cables to convert them to 'rollover cables' (and vise versa) allowing the user to connect to any RYSC serial device using only:
  1. A 'blue Cisco console cable'. Either a USB-to-8P8C cable or the older DB9-to-8P8C cable (possibly attached to a USB-to-RS232 adapter), both work fine.
  2. An 8P8C straight-to-rollover adapter (to convert a straight-through RYSC serial cable to a RYSC Null-Modem cable and vise versa).

Appendix:

To distinguish DTE and DCE, use the following guidelines:
1. DTE is Data Terminal Equipment, it is the output or user-interface. The archetypal DTE is a teletypewriter. Teletypewriters used modified typewrites to print the output of a remote typewriter's keyboard input to a local printer (and vise versa).
2. DCE is Data Communication Equipment. The archetypal DCE is a modem on in a teletype environment, or any device that connects the end-user interface to a communication channel or media (phone line, LAN, radio waves, etc.)
RYSC 8P8C plug specification outline:
- The RYSC 8P8C plug is populated on pins 3, 4, 5, and 6.
- Pins 3 and 6 on the 8P8C connector will be connected to Transmit and Receive.
- Pins 4 and 5 on the 8P8C connector will both be connected to Signal Ground.
Data pins on sub-miniature-D-shells (for a minimal 'three-wire serial connection'): Sub-miniature-D-shell (DB9 and DB25) connectors carry Transmit and Receive on pins 2 and 3. Signal Ground on a DB9 is pin 5. Signal Ground on a DB25 is pin 7 .
Flow Control pins on sub-miniature-D-shells:
- DB9: pins 4 and 6 (RTS and CTS), pins 7 and 8 (DSR and DTR).
- DB25: pins 4 and 5 (RTS and CTS), pins 6 and 20 (DSR and DTR).
RYSC adapter Tx/Rx pinout:
- On DB9 RYSC adapters, a DTE device DB9 pin 2 connects to Black wire (USOC 8P8C) and DB9 pin 3 on the Yellow wire (USOC 8P8C).
- For DCE, the Tx/Rx connections are reversed from their DTE configuration.
- For DB25, the Tx/Rx connections are reversed from their DB9 configuration.
- The previous two rules combined correctly imply that a DB9 DTE and a DB25 DCE have congruent transmit/receive color-to-pin-number assignments.
RYSC cable pinouts:
1. 1. For a 'straight-through' serial connection, use a 'rollover cable' between two RYSC adapters. A rollover cables two ends are pinned in reverse of each other. That means when both ends of a rollover cable are share alignment and orientation, the pin order will be 'mirrored' or 'flipped'
2. For a 'Null-Modem' serial connection, use an ordinary Ethernet patch cable (or an even number of daisy-chained rollover cables) to connect the two RYSC adapters.

Bibliography:

Yost serial device wiring standard http://yost.com/computers/RJ45-serial/

serial wiring for the confused http://aplawrence.com/Unixart/serial.art.html

Zonker's minor scroll of console knowledge http://www.conserver.com/consoles/msock.html