Many people have said it can't be done, and why don't you just buy a second hand PC?

• Firstly, yes it can be done - and this page shows you how to do it.
• Secondly, this is much cheaper than buying a second hand PC (along with all the headaches of windows...).

The Problem:

The reason why the Cybot programming software will not upload software to the Handset under Virtual PC on a Mac is simple. The handset uses a crude method of interfacing to an RS232 port (see circuit diagram below). That is, it does not produce proper RS232/422 levels, and the Mac doesn't like that as RS422 is more sensitive to levels.

The solution:

Simply use a MAX232 line driver/receiver chip to invert the signal and produce the correct levels.

OK, heres what you will need:

• Computer (Minimum requirements):
• Macintosh running OS 9.2.2
• G3 processor
• 128MB RAM
• Virtual PC 3.0
• One serial port

Electronics components:

• 1 x MAX232 Integrated circuit
• 4 x 1uF electrolytic capacitors (C1 to C4 in the circuit below)
• 1 x 470uF electrolytic capacitor
• Veroboard

The working adapter circuit:

How it works:

RS232 is actually a little less fussy than RS422. RS232 will see anything below about 0.25V as a logic 1, therefore the crude circuit used in the Cybot handset will work on RS232 over a short distance. However, RS422, having a wider noise margin, is more fussy that the levels be correct.

For true RS232 or RS422 signalling, the signals should swing between +5V to +12V for a logic 0, and -5V to -12V for a logic 1.

Notice, that I have refered to a logic 1 as being a negative voltage. That is correct, and I'm not sure why the original spec for RS232 decided that a negative voltage would represent a logic 1.

The adapter circuit does two things. First, it provides a buffer that is specified for + or - 12V signals. This buffer also inverts the signal coming from the Mac or the Handset (as RS232 is negative logic, remember). So, we have to invert it again, and provide the correct RS232/422 voltage levels.

The Cybot Handset circuit: (Found at www.cybench.co.uk)

If you are using a Mac with the old RS422 port (8 Pin mini DIN) see the table below. If you are using a Keyspan USB to RS422 adapter, also see the table below.

If you are using a USB to RS232 adapter, you may or may not have success, depending on the brand of adapter, and the Mac software driver for it.

Keyspans should be OK...

Wiring RS422 to RS232:

To use an RS-232 device on a Mac, you will need to convert the Mac's RS-422 signal. To do that, just follow the table below. Connect the serial cable that comes with the Handset to the PC 9 pin MALE plug of the cable below:

Mac 8 Pin RS422 port	PC 9 pin D type MALE plug
HSKout, 1	DTR, 4
HSKin, 2	RTS, 7
RX-, 5	RX, 2
TX-, 3	TX, 3
GND, 4	GND, 5

NOTE: Ground RX+, leave TX+ floating.

Screenshot:

See? It works!! (click image for larger view).

The protoype on breadboard:

Coming later: construction and installing in the handset.