Retromaster’s Electronics Projects

…related to old computers and other assorted stuff…

Archive for July, 2010

UFE A1200 Keyboard Daughterboard Design

Posted by retromaster on July 28, 2010

After the initial release of information on UFE, quite a few people asked about A1200 support. So, here is the early result of my design efforts for an UFE A1200 keyboard daughterboard.

The board is designed to plug into the keyboard flex cable socket on the A1200 motherboard (see the edge connector on the bottom of the PCB). The flex cable from the keyboard goes into the connector on the top left side of the board. So, this board acts as a kind of pass-through.

A 40-pin PIC MCU sits on the right side and is responsible for scanning the keyboard and translating keycodes into the I2C protocol for UFE communication. A couple of 74ls245 chips are placed in between the keyboard and motherboard connectors. These are used to disable the column drivers on the Amiga side when UFE takes over control of the keyboard. This way UFE can scan the keyboard without interference from the Amiga keyboard MCU.

This should all work in theory, based on my understanding of the A1200 schematics and the reverse-engineered A1200 keyboard schematics. Of course, there is a decent chance it could fail, so that’s why there are no schematics accompanying this post. I’ll build the PCB soon and write the firmware for the PIC and see if it actually works :). I haven’t checked the A600 schematics yet, but there is a good chance that this will also work with the A600 without modification.

Part of the challenge here was to make everything fit in the rather limited space. That’s why the board ended up being double-sided. It does not require plated-through holes, however, and there are only a few vias that can easily be handled by soldering wires on both sides. These measures should help keep the cost to a minimum. The current board layout also requires the A1200 metal shield to be removed, but this may perhaps be avoided, by elongating the board even further.

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UFE Page Up!

Posted by retromaster on July 10, 2010

I’ve just posted the UFE page, which contains detailed info, photos, a video and schematics.

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UFE New PCB Assembled and Working

Posted by retromaster on July 6, 2010

Over the last couple of weeks, I’ve managed to assemble the new UFE board and make the necessary changes to the firmware to make it work with the PIC32MX575. I’ve also mounted the board in the floppy slot of an A500 to see how it would actually look. The result is quite nice and it is quite practical to operate with the A500 top cover closed. I’ve had to hot glue a couple of threaded posts to the base of the A500 case to be able to screw the board, but other than that, no case modding is necessary.

I am a little disappointed with the PIC32MX575 though. First of all, the I2C module has an embarassing bug which causes the module not to assume control of the output pins properly. To add insult to injury, the workaround specified in the errata document seemed to be insufficient in my case. In addition to manually declaring the pins as output, they also needed to be configured as open-drain, otherwise it did not work. Another issue (that still remains unresolved), is that I could not get the “IDLE” power save mode to work properly. The behaviour here seems to be different than the PIC32MX460, but I could not figure out what exactly is different. The IDLE mode is used by the UI code to wait for the vertical blanking period for video output. The code that worked fine on the 460 does not seem to work on the 575, so I’ve had to (hopefully temporarily) replace the IDLE mode with busy-wait loops.

Nevertheless, most of the basic functions of the UFE work fine in the new board. There is one remaining problem with the write clock recovery circuit that I could not get the component values right. Hopefully, I should be able to sort out that problem tonight. Afterwards, the first order of business will be to create a video of the UFE in operation and put up a new project page for it.

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