Hotshot II schematic?
Hotshot II schematic?
Does anyone know if a schematic for the Hotshot II exists somewhere?
Re: Hotshot II schematic?
I don't know of a schematic that is available but it is a small board.
Do you have one in your possession that you can examine?
Do you have one in your possession that you can examine?
Re: Hotshot II schematic?
sorry no, just been going by some of the high resolution photos that i found on "the net". from what i can tell, it's got some PALs on board to generate RAS/CAS as well as some address decoding circuitry. i should be able to reverse engineer something with SRAM instead, but i thought i'd at least try to find a schematic...Brutman wrote:I don't know of a schematic that is available but it is a small board.
Do you have one in your possession that you can examine?
probably can use my 512k mem side car as a starting point...
https://hackaday.io/project/171128-ibm- ... sion-board
Re: Hotshot II schematic?
I have one here that I can buzz out for you. I don't want to do the entire thing because that would be error prone, but if you have a specific area of interest I can examine it.
(I should probably check to ensure it is the correct revision.)
I am not an electrical engineer but I do pretend to be able to read simple TTL diagrams. My understanding of these boards is that they pass all memory references to the first 128KB to the system board and backfill the remaining 512KB. Accesses above 640KB continue to be sent to the system bus for obvious reasons. An SRAM implementation is simpler and slightly faster as there are no DRAM refresh cycles to get in the way.
The PALs are probably just there to determine which memory accesses to let through and which ones to send to "local" RAM. The HotShot boards also had a clock/calendar so there was additional I/O port space grabbed by the board.
(I should probably check to ensure it is the correct revision.)
I am not an electrical engineer but I do pretend to be able to read simple TTL diagrams. My understanding of these boards is that they pass all memory references to the first 128KB to the system board and backfill the remaining 512KB. Accesses above 640KB continue to be sent to the system bus for obvious reasons. An SRAM implementation is simpler and slightly faster as there are no DRAM refresh cycles to get in the way.
The PALs are probably just there to determine which memory accesses to let through and which ones to send to "local" RAM. The HotShot boards also had a clock/calendar so there was additional I/O port space grabbed by the board.
Re: Hotshot II schematic?
yea i figured that could use my sidecar sram board as a starting point. i didn't see any dram controller on the board, so i was assuming the PAL was generating both the address decoding and RAS/CAS for refresh. thanks for the offer on doing some testing, but i think i'll just jump directly in and try my hand at the SRAM version...Brutman wrote:I have one here that I can buzz out for you. I don't want to do the entire thing because that would be error prone, but if you have a specific area of interest I can examine it.
(I should probably check to ensure it is the correct revision.)
I am not an electrical engineer but I do pretend to be able to read simple TTL diagrams. My understanding of these boards is that they pass all memory references to the first 128KB to the system board and backfill the remaining 512KB. Accesses above 640KB continue to be sent to the system bus for obvious reasons. An SRAM implementation is simpler and slightly faster as there are no DRAM refresh cycles to get in the way.
The PALs are probably just there to determine which memory accesses to let through and which ones to send to "local" RAM. The HotShot boards also had a clock/calendar so there was additional I/O port space grabbed by the board.
sidenote: any recommendations other than adding a clock to the design?
Re: Hotshot II schematic?
Were PALs able to do that kind of thing? My understanding of PALs is that they provided pretty simple logic. Emulating a DRAM refresh controller seems beyond their capability, as that would require counters or timers.
Some of the designs that fit in that slot added room for an 8087 or added dedicated RAM for the video buffer, which effectively removes the hole in main memory that we all hate so much. The 8087 is interesting but would be weird because of the NMI handling on the Jr, while fixing the video buffer hole might break compatibility with programs that use the extended video modes.
I can't think of anything else interesting to tuck under there.
Some of the designs that fit in that slot added room for an 8087 or added dedicated RAM for the video buffer, which effectively removes the hole in main memory that we all hate so much. The 8087 is interesting but would be weird because of the NMI handling on the Jr, while fixing the video buffer hole might break compatibility with programs that use the extended video modes.
I can't think of anything else interesting to tuck under there.
Re: Hotshot II schematic?
you are correct that the PALs can't do the DRAM refresh alone. the PALs are used for doing the control signals and address signals. from the pictures i have for the HotShot II, there is a CD4040 in the top right hand corner next to the PAL chips. the CD4040 is a "12-Stage Binary Ripple Counter" which would generate all the timing needed to have the PAL logic step through and refresh the DRAM.Brutman wrote:Were PALs able to do that kind of thing? My understanding of PALs is that they provided pretty simple logic. Emulating a DRAM refresh controller seems beyond their capability, as that would require counters or timers.
Re: Hotshot II schematic?
If you are interested in picking up a Hotshot II to check out for yourself I did spot this https://www.ebay.com/itm/Vintage-IBM-PC ... 3643117847
Re: Hotshot II schematic?
dandy thanks! i'll bid on that!Gremlin5 wrote:If you are interested in picking up a Hotshot II to check out for yourself I did spot this https://www.ebay.com/itm/Vintage-IBM-PC ... 3643117847
Brutman - if i win the bid on that, and write up some documentation with pictures, would you be interested in adding it to your accessory pages?
Dave
Re: Hotshot II schematic?
I'd be willing, but honestly I should just get off my rear-end and get the documentation that I have scanned and posted.
I'm a few years behind.
I'm a few years behind.