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Feasibility study for a TMS9900 system ?


lezanderson

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I was thinking of doing a Feasibility Study on a New TMS9900 (TiI99/4A) Type system. Possibly with the following spec:

Looking at the possibility of making a replacement (low cost) Ti/99/4a motherboard ??

 

 

TMS9900 CPU clocked at 16/4MHz 16MHz input 4MHz bus, Zero wait states on RAM/ROM

 

 

TMS9900 CPU
TIM9904A Clock gen
TMS9901 PIO x 2
TMS9902 SIO x2
EPM7128SLC84 as Glue logic (possibly 2pcs)
RAM 128kx8bit x 4 pcs (512k sram 100ns or faster)
NVSRAM (DS1245 128kx8bit 2pcs) 256k 70 or 100ns
ROM
V9958 Video 192K Video RAM PAL/NTSC RGB & Composite output
SN76489 sound 2pc (Left / Right sound output)
SAA1099 Sound PSG
PS/2 keyboard/ Mouse
8255 for CF Card reader
8255 for PATA IDE interface
RTC Real Time clock
AM9511A 4MHz Maths co-processor

cost for the ICs about $40 (£28)

If it could be squeezed onto a double sided PCB (300mm x 160mm or so) then the PCB should only cost about £15

Connector,buttons,switches,IC sockets etc about $10 , £7

So total cost would be about £50, $75 ??

As all the ICs are still readily available it shouldn't be to difficult to source everything !

 

The Hard part is obviously design/testing it, and programming the CPLD (VHDL/Verilog) !!

 

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If you're going to use a PLD, why not go for the equally priced, but much more capable MAX10, and program the entire system in there, CPU and all? With today's FPGA's a SoC solution is the best way to go for something like this.

 

Plus, the new MAX10's have built-in user flash and SRAM, so the console ROM's and main memory could also be located on-chip. Fewer chips equals cost savings.

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The Two CPLD's I'd consider for glue logic are the : EPM7128SLC84 and the EPM7032SLC44, 128 & 32 Macrocells respectively both can be got for $2.0 each .. much cheaper than an FPGA IC. They can also be programmed in situ with a low cost MAX Blaster programmer about $7.0 each ?

 

A rough 'DRAFT' breakdown of cost for ICs

 

TMS9900 CPU $2.50 each
TIM9904A Clock gen $2.5 each
TMS9901 PIO x 2 $2.0 each
TMS9902 SIO x2 $2.0 each
EPM7128SLC84 as Glue logic (possibly 2pcs) $2.0 each
RAM 128kx8bit x 4 pcs (512k sram 100ns or faster) <$1.0 each
NVSRAM (DS1245 128kx8bit 2pcs) 256k 70 or 100ns $2.0 each
ROM about $1.0 each or less
V9958 Video 192K Video RAM PAL/NTSC RGB & Composite output <$5.50 each
SN76489 sound 2pc (Left / Right sound output) $0.50 each
SAA1099 Sound PSG $1.50 each
PS/2 keyboard/ Mouse (use a cheap micro-controller <$1.0)
8255 for CF Card reader $1.5 each
8255 for PATA IDE interface $1.50 each
RTC Real Time clock $2.50 each DS12C887 ??
AM9511A 4MHz Maths co-processor $2.50 each

 

Most of the Chips would be Working Pulls and some NOS !

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