In 1993 I started to outgrow my PowerBook 140. It was, and still is, a great little machine, but I found myself more and more limited by it's small screen, relatively slow processor and 1-bit outlook on life. It was also by then tied to my desk running a BBS, so I missed the benefits of a portable for which I had bought in the first place.
I therefore decided to buy a PowerBook 165c. As well as being a faster portable with an FPU and colour, it's main appeal was one capability left out of the early PowerBooks, the ability to add an external monitor and increase it's screen area to up to almost three times that of the PowerBook alone.
The external monitor port of a 165c can drive monitors as big as an Apple 16", but such a monitor from Apple was then prohibitively expensive But according to the specs it should also be able to drive the same number of pixels on an SVGA monitor, for a fraction of the price of the Apple monitor. All I needed was an appropriate cable.
The circuitry was already in the Mac - all I needed was a suitable connector or cable. One shop I asked at suggested I try CSC parts where I was able to buy a small black plastic converter, a block 3cm x 3cm x 1cm with a male VGA 15 pin D connector on one end and a female 15 pin Mac D connector on the other, for only $29, which looked like just the thing.
Unfortunately it wasn't. It was wired to make the Mac think a VGA monitor is a Mac RGB 13" monitor, as the video signals for the two are essentially the same. But the Mac 13" monitor is only 640 by 480 pixels. When I connected it to an SVGA monitor it was useless, with the Mac still thinking it was connected to a Mac 13" and so only using the VGA capabilities of the monitor.
A quick search among Mac tech notes told me the reason. Although the signals for the Mac RGB 13" monitor and a VGA monitor are pretty much the same - which makes sense, if only because it saves Apple money when shopping for parts - the wiring for Mac to 13" and Mac to VGA/SVGA is subtly different.
Among the 15 pins of a normal Mac D connector, as well as pins for the colour signals, sync signals and ground lines, there are three pins (the sense lines) used to tell the Mac what sort of monitor is connected. And the wiring of these sense lines for Mac RGB 13" is different from that for VGA/SVGA. By wiring these to ground or to each other a cable can tell the Mac exactly what sort of monitor the Mac is connected to.
There was no way I could modify the connector I had just bought, so it was back to CSC parts to get the bits & pieces to make my own cable. I needed one DB-15 connector, one VGA D connector, the casing for each of these and 6' of 13 core cable, costing altogether about $25.
Then I set to work soldering. It turned out I could have got by with just 9 core cable, as not all the pins are used. The table below gives details of which pins to link to which:
Mac Pin VGA Pin Name Signal 1 6 RED.GND Red ground 2 1 RED.VID Red video signal 3 /CSYNC Composite sync signal 4 SENSE2 Monitor sense 2 5 2 GRN.VID Green video signal 6 7 GRN.GND Green ground 7 tied to pin 10 SENSE1 Monitor sense 1 8 n.c. Not Connected 9 3 BLU.VID Blue video signal 10 tied to pin 7 SENSE0 Monitor sense 0 11 C&VSYNC.GND Ground for CSYNC & VSYNC 12 14 /VSYNC Vertical sync signal 13 8 BLU.GND Blue ground 14 10 HSYNC.GND HSYNC ground 15 13 /HSYNC Horizontal sync signal
Note that pins 7 and 10 on the Mac connector need to be tied (connected) together to tell the Mac it is connected to a VGA or SVGA monitor. Pins 3, 4, 8 and 11 on the Mac should be left unconnected.
It took about an hour to solder the cable to both connectors, partly as I'm a bit rusty with a soldering iron, but also as it was a fiddly job to do, with the pins on the VGA connector being close together and difficult to reach. Not as difficult as some soldering jobs I have attempted, but not recommended to anyone at all unfamiliar with a soldering iron.
And it worked first time, or at least first time I connected it to an SVGA monitor, as the first monitor I tried was a fairly ancient VGA. After experimenting with various monitors in the office I eventually bought a Philips 14" VGA/SVGA for home use, while sticking with a spare Apple 12" in the office (which connects directly to the 165c external video adapter).
A similar cable will work with many other recent Mac models. On portables with external video, the LC475, Quadras and Centrises it provides both VGA (640 x 480) and SVGA (600 x 800) output, while with the LC, LCII, LCIII, IIvi and IIvx, and the x100 PowerMac DRAM (built in) video it provides just VGA (640 x 480) resolution.
A PowerMac VRAM expansion card provides VGA (640 x 480) and SVGA (800 x 600) output, while a PowerMac AV card can drive a VGA monitor at up to (VESA) 1024 x 768. The latest PowerMacs, e.g. the 7500 and 8500, support up to 1280 x 1024 at 75Hz, while Macs (and clones) with video cards may support even higher resolutions and faster refresh rates with this cable.
If your Mac is one that has a choice of resolutions you choose between them in the 'Options...' dialog of the Monitors control panel (see figure), from where you can also specify the gamma for the monitor. If your Mac supports more than one monitor you can also use this control panel to independently set the bit depth of the two displays and let the Mac know how the screens. And the same cable can be used to connect a PowerBook to a variety of external displays, for example LCD panels and projection devices, almost all of which have VGA/SVGA connectors.
One curious feature of the PowerBook 165c is that, because of memory considerations, the internal (LCD) video is a lot slower than the built in video of comparable '030 desktop Macs, and switching to fewer colours or B&W does little to speed it up. External video performance is much better, over twice as fast in some operations at 256 colours and even faster with fewer colours on screen.
So for a lot less than $100 dollars and an hours soldering I can connect my new Mac to the equivalent of an Apple 16", increasing the screen area by over 180%, for only a fraction of the price of the equivalent Apple monitor. It also greatly increases the portability of my Mac, as I can take it almost anywhere and know it will work with almost any current monitor*
After almost a year of using two screens I cannot now imagine working solely on a Mac to which I could not connect a second screen for design or development work. But the greatest benefit? It's looking over a co-workerÕs shoulder and remarking "You know, that job would be a lot easier on two monitors", quickly followed by "Really? I didn't realise people still use operating systems that only support a single monitor!".
This article appeared in the July 1994 edition of the Hong Kong Mac User Group newsletter.
Reference: Apple Technical Note HW 30 - Sense Lines
© John Blackburne, johnb@hk.super.net, 6th September 1996
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