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--- builderpages:brian_osullivan:start [2019/07/15 23:27] – Initial import from Wayback Machine
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 In the meantime I have built myself an SMD oven with my own control gear. Can't wait to use it on that tricky VGA chip package!
+----
+UPDATE 17 Sept 2020: That video chip is extremely difficult to solder on. Ended up destroying two chips and the board is now stuffed. The video memory is also REALLY hard to find (I pulled some out of a working card in the end). I would like to see the board sold with the chip pre-soldered to assist those of us who don't have the capability to solder these parts properly. Maybe a new VGA board design could be considered? Perhaps use an Altera FPGA dev board - not my area of expertise unfortunately. I like that Sergey designed this board - but I think a new solution needs to be found for 8 bit VGA cards.
+----
 Managed to work out how to get an old 16 bit video card to work in 8-bit mode by researching the original reference circuit from the chip datasheet and finding which jumper was the most likely one to set (as there is no documentation at all for the card that I could find).
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 For now I will just turn on and press reset.
+UPDATE: 17-Sept_2020 - nope, changing to ALS parts made no difference. Subsequently built Sergey's other 8088 board and found it exhibits the same issue exactly. That leaves the BIOS perhaps? I took a look in there and it fails at the same place on both boards - I have given up on this one for now - if anyone else has the same issue and finds a solution I am all ears.
 Note: also occasionally stops after a few hours of uptime. Managed to take a look at the system bus with my oscilloscope when in this state and noted that the processor was running, but the ISA bus had no activity on the address and data lines. Suspect timing issue as above - or possibly the bus transceiver circuit is stuck in high impedance state. It is a rare fault so will tackle the keyboard controller first in the hope the two issues are related.
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 Not bad for $5.
+//**SBC-188 v2**//
+Someone was selling a surplus SBC-188 v2 board near my location so I bought it and started a new project.
+COVID made parts deliveries fairly sporadic so this one has been meandering slowly but steadily to completion. The floppy controller has been a challenge - and getting crystals are taking forever as well.
+Some parts must be ALS type - but I am finding these are not generally available new anymore from most of my regular suppliers - at least in DIP through-hole packages….. Three ALS chips left to source….
+c188 microprocessors proved to be easy to source - I was expecting them to be rare but they seem to be all over the place. However, the faster chips are the most common - the 16MHz version the board is designed for was hard to find. Weirdly I ordered 2 x 20 MHz parts - but when they arrived they were actually 16MHz parts - so happy days by complete accident!
+All soldering is completed now - just waiting for the straggler parts to come in, burn the rom and say a silent prayer to the retro computer gods before powering up and testing.
+-Nov-2020 - Board is completed and alive! A few issues at the start as follows:
+At first it wouldn't start reliably at all, so I reduced the clock speed from 16MHz to 10MHz. This seemed to work. Spent some time cleaning off flux and debris from the solder side to hopefully solve that issue. The 2 x Oscillator can is positioned perilously close to the pins of the adjacent chips - you have to take care not to touch them when in final position. Possibly the spacing on the board could be changed - but there is a completely redesigned v3 board so unlikely to happen.
+At this stage the board would start but stop every time at the clock/NVRAM setup stage. This baffled me for a whole day. In the end it turned out to be the VT100 emulator terminal (Geoff G) I was using. There seems to be a bug in the terminal firmware where it wouldn't scroll when it got to the bottom of the screen - so I could not see the prompts. I surmised this was the case when I discovered that if I hit enter exactly 11 times, the controller would move to the next step in the bootup process. I waded through the BIOS code and found that the NVRAM setup for the board has exactly 11 items. The workaround was to reset the terminal at this point so it would clear the screen and start from the top again. I am not intending to use the terminal on this board after initial testing, so will leave that for now. Interestingly the terminal later had no issue with scrolling the screen once it had booted into DOS.
+Which, of course, brings me to booting into DOS…. After the usual fun trying to get a working boot floppy made, I found it wouldn't boot. But this time I had a real good idea of what the issue after having a similar experience with the DiskIOv3 ECB board (see above). The issue is that for a 1.44Mb floppy drive you need extra speed to handle the higher data transfer rate through the floppy controller. I had still left the board on 10MHz - so changed back to 16MHz oscillators and now it booted off the floppy ok. Interestingly, all my board cleaning and reseating of ICs while investigating the serial terminal issue seemed to have resolved the issue of not starting at 16MHz - because now it is running correctly every time I boot.
+Next was the PPIDE and CF card interface. I had an existing working set of these, including a CF card with DOS 6.22 installed. But the bios just wouldn't boot from it - or even recognise it. I had a CF card from my Z80 project with CPM on it plugged that in and the bios recognised that ok. Booted off the floppy, used the supplied Fdisk86 utility for the SBC-188 to create a DOS partition, and now the CF card works as C drive ok. I haven't managed to get it to boot off the CF card yet - but I am not expecting that to be a problem. I am making a parproppio board to go with the SBS-188 - so the CF card won't be needed in the long run.
+That's it for now - I will add some documentation below when I finish the project to record poorly documented items for the v2 SBC-188 board - namely what the boot sequence actually does so you can work out what part it is stopping on and also the jumpers.
+Happy for now. This board was easier to get going than most. Partly because the xi8088 and other ECB boards above made it easier for me to recognise where I was going wrong.