Psion Sidecar Part II

I’m going to dive in a bit on the Psion Sidecar that I covered last week and add some details to explain the RS232 connections and the switches on the Sidecar.

Male DB9 Connector

Pin	Function	I/O Direction
1	Data Carrier Detect (DCD)	Input
2	Receive Data (RD)	Input
3	Transmit Data (TD or SD)	Output
4	Data Terminal Ready (DTR)	Output
5	Signal Ground (SG)
6	Data Set Ready (DSR)	Input
7	Request to Send (RTS)	Output
8	Clear to Send (CTS)	Input
9	Ring Indicator (RI)	Input

Sidecar DB9 Pinout

The silkscreen and case markings were confusing me at first. It was a bit difficult to understand which switch position was for a straight Data Terminal Equipment (DTE) connection and which was for a Data Communications Equipment (DCE) connection. The silk screen on the PCB indicate that when both switches are toward the DB9 connector, that it is a straight DTE connection and when they are away from the DB9 connector, they are in the crossover/null modem DCE configuration. The case indicates that if they are to the left, as you look at the switch, then it is straight through and to the right is crossover configuration. These two were not in agreement.

Using an ohm meter to trace the connections through to the Raspberry Pi, it was apparent that the case was more correct but the opposite of what my thought was regarding the symbols. I thought that the straight arrow indicated that the DB9 was in a DTE pinout and the crossover symbol as the DCE connection. It is actually the opposite. I think that Kian may be indicating what device it is connecting to rather than what the DB9 pinout of the Psion Sidecar is when the switch is in a particular position.

Switch Positions

• Left – DCE Pinout: Use when connecting to a PC or another device with DTE pinout.
• Right – DTE Pinout: Use when connecting to the Psion, modem, or other device with a DCE pinout.

Pin	DB9 TX:RX RTS:CTS (Right DTE)	DB9 TX:RX RTS:CTS (Left DCE)	SP3232E TX:RX RTS:CTS (Right DTE)	SP3232E TX:RX RTS:CTS (Left DCE)	Raspberry Pi TX:RX RTS:CTS (Right DTE)	Raspberry Pi TX:RX RTS:CTS (Left DCE)
1	Not Connected	Not Connected	Not Connected	Not Connected	Not Connected	Not Connected
2	RD	TD	13->12	14<-11	10 GPIO15	8 GPIO14
3	TD	RD	14<-11	13->12	8 GPIO14	10 GPIO15
4	Not Connected	Not Connected	Not Connected	Not Connected	Not Connected	Not Connected
5	SG	SG	15	15	6	6
6	Not Connected	Not Connected	Not Connected	Not Connected	Not Connected	Not Connected
7	RTS	CTS	7<-10	8->9	11 GPIO17	36 GPIO16
8	CTS	RTS	8->9	7<-10	36 GPIO16	11 GPIO17
9	Not Connected	Not Connected	Not Connected	Not Connected	Not Connected	Not Connected

Properly shutting down the Psion Sidecar

To properly shutdown the Raspberry Pi in the Sidecar, open the Hermes or other terminal application. Connect to the Sidecar using telnet on port 23. Once connected, login and issue the command “sudo shutdown now“. Once the green light on the Raspberry Pi stops blinking, you may press the power button to turn the unit off.

Conclusion

I hope this is helpful in understanding how properly shutdown the Psion Sidecar and how to use the switches. Typically the switches will be in the right position to allow communication with a Psion 5mx device using the Psion BB9 cable.

Kian’s design is very nice as it allows the Psion Sidecar to be used for other things without the need of a null modem to connect it to another device. The only thing that you may need is a F-F gender changer and DB9 to DB25 adapters. This makes it a versatile device to connect other devices.