• Please review our updated Terms and Rules here

Powertran Cortex

Jim Hearne said:
A quick look at your PCB and I would say you need more 0.1uf decouplers, at least one for every chip, as close between 0v and 5V as you can get them.
Click to expand...

OK, I'll try to fit some more in. I'm using 1uF tantalums to decouple, is that a good choice? Also two 100uF mini elco's thrown in for good measure. This seems to work out okay on the breadboard. Or am I being silly?

Jim Hearne said:
Silly question, where does the power connect ?
Click to expand...

Power is drawn from the USB host. The circuit should draw less than 500mA. For the USB bridge I use see:
http://www.elektor.com/ft232r-usb-serial-bridge-bob-110553-91
This power source has worked well on the breadboard. Perhaps I need to add a 5.5V zener diode from Vcc to GND as a circuit protector.

Thanks for your input!
 
pnr said:
OK, I'll try to fit some more in. I'm using 1uF tantalums to decouple, is that a good choice? Also two 100uF mini elco's thrown in for good measure. This seems to work out okay on the breadboard. Or am I being silly?

Power is drawn from the USB host. The circuit should draw less than 500mA. For the USB bridge I use see:
http://www.elektor.com/ft232r-usb-serial-bridge-bob-110553-91
This power source has worked well on the breadboard. Perhaps I need to add a 5.5V zener diode from Vcc to GND as a circuit protector.

Thanks for your input!
Click to expand...

Decouplers are normally 0.1uf Ceramics to filter the high frequency noise from the logic.
I'm not sure if tantalums are as good at high frequencys though they are much better than electrolytics are.
Leave the Electrolytics you have in for low frequency filtering.

I use USB to TTL serial cables like these a lot at work.
http://uk.farnell.com/ftdi/ttl-232r-5v-we/cable-usb-ttl-ser-conv-5v-wire/dp/1740364
They are great for hooking up directly to a TTL serial port on a micro.

Can i suggest putting a couple of pads for a terminal block or a connector on the 5V rail, also maybe some pads for the serial port.
It would give people some other options if you end up selling any of the pcbs.


A diode or power Zener across the supply is always a good idea.
It's about the first thing i connect on any prototype, especially if it's being powered from a bench supply with some test leads.
They are known as dickhead diodes where i work.

Jim
 
Things that are always useful on any microcomputer board are :

Standard Power Jack
power ON LED
ON/OFF switch
Safety Fuse ?? perhaps
7805 voltage regulator

Also it's good to use standard connectors like 9 pin D type for RS232 .. though the RS232c standard didn't specifiy any perticular connector the 9 pin D Type became standard !
 
Most Microcomputer boards tend to need :

A Generic 2.1mm power Jack so a low cost PSU can be attached 9/12V ?
7805 Regulator
Power on LED
Safety Fuse...Perhaps but the 7805 should be enough safety ?
ON/OFF Switch

Standard D-Type connectors for things like RS232 ?
 
ti99/4a said:
Most Microcomputer boards tend to need :

A Generic 2.1mm power Jack so a low cost PSU can be attached 9/12V ?
7805 Regulator
Power on LED
Safety Fuse...Perhaps but the 7805 should be enough safety ?
ON/OFF Switch

Standard D-Type connectors for things like RS232 ?
Click to expand...

Thank you for your input! The mini cortex is designed to have a USB interface, hence the D type connector is less appropriate. USB also provides a regulated 5v power source, that's why you don't see a 7805 or equivalent regulator. The power led is already there.

I think I will add a header to accommodate other interface wishes.
 
Stuart said:
U10. Feel a bit uncomfortable that CRUCLK isn't involved in deriving the /CE. I guess though that if /MEMEN is high then it must be a CRU cycle (or an external instruction, which you aren't using by the looks of things).

Stuart.
Click to expand...

This comment was naging me and I just realised why: Unix and xinu do use the idle instruction. Considering the very partial cru adres decoding I guess that I was lucky that the breadboard verslons worked. i'll add a ls138 external instruction decoder to the mini cortex.
 
pnr said:
This comment was naging me and I just realised why: Unix and xinu do use the idle instruction. Considering the very partial cru adres decoding I guess that I was lucky that the breadboard verslons worked. i'll add a ls138 external instruction decoder to the mini cortex.
Click to expand...

Have you got room to add another GAL, and implement it in that? Then have some spare GAL inputs/outputs for future tinkering. And as you're decoding the external instructions, is it worth using /LREX to do the single step and /CKON/CKOFF to switch the memory mapper on/off (with the spare flip-flop), as per the Cortex? Will need to do some rework of the PCB of course. ;-(
 
Stuart said:
Have you got room to add another GAL, and implement it in that? Then have some spare GAL inputs/outputs for future tinkering. And as you're decoding the external instructions, is it worth using /LREX to do the single step and /CKON/CKOFF to switch the memory mapper on/off (with the spare flip-flop), as per the Cortex? Will need to do some rework of the PCB of course. ;-(
Click to expand...

Not sure I can fit a 24 pin part, a 16 pin part should fit. I think I need the spare flip-flop for the LREX interface als well, right? What is beter in that case, LREX or CKON/CKOFF? I would guess the former as there is no vintage software that uses the cortex mapper?

Also, I'm more and more tempted to shift most stuff over to the left and squeeze in an F18A socket in between the CF card and the CPU/MEM chips.
 
Something slightly off-topic :

*** Sourcing ICs from China *** an idiot's guide :

some of you may have noticed that I was selling some TMS9900 kits on ebay ? My little experiment to get people interested in hardware design etc has now finished !

These kits of ICs where sourced from two Chinese suppliers : G&C supermarket and Funkward-tech. I didn't test any of these ICs myself (though the supplier said they had, ...as they would !) However I did send a small sample to Stuart and he found most to be OK ? Bizarley the ICs from G&C looked like brand New (NOS) where those from Funkward-tech were clearly pulls.

I know a lot of people have problems with sourcing these ICs from China , but I've found them to be pretty good, the few DUFF ICs I received where promptly resent and replaced with new..

If anyone needs help with sourcing ICs please just ask.
 
Below is a rough guide to the prcies I paid for some ICs, this may be useful when costing a project ?

Approximate wholeslae price for some common ICs

Wholesale prices:


CPUs

TMS9900 $3.0 each
TMS9995 <$7.0 each
TMS99105 <$20 each

TMS9901 $2.50 each
TMS9902 $2.0 each
TIM9904A $2.50 each

TMS9911 DMA $2.50 each
74LS61x Memory Mapper $2.50 each

TMS FDCs <$10 each .. ask for price
TMS9909 / TMX9909
TMS2797 FDC

Static RAMs (DIP)

HY6264 8Kx8bit 70ns/100ns $1.0 each
HY62256 32Kx8bit 70ns/100ns $1.0each
HM628128/TC551001/KM68000 128Kx8bit 55ns/70ns/100ns $1.0 each
KM684000/HM628512/K6T4008 512Kx8bit Static RAM 70/55ns $3.50 each

Static RAM (SDIP)

UM61256 15ns DIP <$1.50 each
UM61512 15ns DIP <1.50 each

NVSRAM (DIP) : DS1250/DS1245 etc
32Kx8bit / 128Kx8bit /512Kx8bit $2.0 each


EPROMs/EEPROMs

27C32 DIP <1.0 each 120/100ns
27C64 DIP <1.0 each 70/120/100ns
27C128 DIP <1.0 each 70/120/100ns
27C256 DIP <1.0 each 70/120/100ns


(DIP & PLCC)
W27C512 64Kx8bit 45ns DIP/PLCC $1.0 each
W27C010 128Kx8bit 70ns DIP/PLCC $1.0 each
W27C020 256kx8bit 70ns DIP/PLCC $1.0 each
29F040 512kx8bit DIP/PLCC $3.50 each PLCC $1.0 each

Video Processors

V9958 DIP64 <$5.0 each
D72020/D7220 DIP40 $2.0 each
V6366 PLCC68 $3.50 each
EF936x GDP DIP40 <$15.0 each
R6545 DIP40 $2.0 each
V9990 Surface Mount <$20.0 each


TMS4465/D41464 100ns DRAMs $0.75 each


Sound Chips

SN76489 DIP16 $0.50 each
SAA1099 DIP18 <$1.50 each
AY-3-8910 DIP40 <$2.0 each
YM2149 DIP $2.50 each
YM3812 DIP $1.50 each


PIO
8255 PIO DIP40PLCC44 $2.0 each : PLCC44 ones $1.0 each


MCUs

AT89C205 DIP $0.75 each
ATMega88 DIP $1.50 each




GALs/CPLDs


GAL22V10/GAL16V8 etc $1.0 each
EPM7128SLC84 $2.0 each
EPM7160SLC84 $10.0 each
EPM7064SLC4 ask ?
 
pnr said:
Not sure I can fit a 24 pin part, a 16 pin part should fit. I think I need the spare flip-flop for the LREX interface als well, right? What is beter in that case, LREX or CKON/CKOFF? I would guess the former as there is no vintage software that uses the cortex mapper?

Also, I'm more and more tempted to shift most stuff over to the left and squeeze in an F18A socket in between the CF card and the CPU/MEM chips.
Click to expand...

Ah, LREX does need a flip-flop by the looks of things. So we're a flip-flop short. If you used it for LREX, then the code for the single-step is just a simple LREX rather than the (6?) or so lines of code you posted earlier? Is that a benefit?

Yes please for the F18A socket. ;-) Have you checked out the F18A website to see which pins you need connected?
 
Is that a benefit?
Click to expand...
A marginal one, but so is CKON/CKOF. Which is preferable?

Yes please for the F18A socket. ;-) Have you checked out the F18A website to see which pins you need connected?
Click to expand...

Yes. Not very many.
 
pnr said:
A marginal one, but so is CKON/CKOF. Which is preferable?
Click to expand...

If it were mine, I'd use the flip-flop for LREX single stepping. The mapper controlled through the CRU latch. As you said before, there is no existing software that uses the mapper.
 
With a bit of Tweaking it could be modified into a Tomy Tutor ??

pnr said:
Here are a draft schematic and a PCB design for the "Mini Cortex". I have a little room left over on the PCB. I've considered adding further memory protection (futile), adding an ethernet chip or an F18A. For the latter I'm not so much interested in the 9918A part, but I find the embedded 9900 GPU intriguing and an F18A may serve as a handy development board to prototype an FPU for the 99105 project. On the other hand, mission creep is usually a progress killer.

Jim, Stuart and Ksarul, I would appreciate your constructive critique of the design and PCB (it has been 35 years since I last did a PCB and those were simple, hand-drawn affairs).

Paul
Click to expand...
 
I'm looking for a supplier to make some double sided PCBs.. does anyone know or can recommend a reputable company ?

I've been told that you can get a good quality 300mm x 160mm Double sided board for £15 each, though you have to order min 10 boards !
 
ti99/4a said:
With a bit of Tweaking it could be modified into a Tomy Tutor ??
Click to expand...

I guess once the F18A is added it is reasonably close to a Tomy Tutor, minus the keyboard, joystick, printer and cassette interfaces. Also, the locations of memory mapped I/O devices are different. I think your biggest hurdle will be to find good schematics and ROM images of a Tomy Tutor, but with that in hand the "tweaking" should be doable.

It also depends whether you want to use Tomy software unchanged or are able to tweak the software. In the latter case, less tweaking of the hardware is needed. in the former case, you might be better of doing an exact copy of the Tomy Tutor, only changing the 9918A for an F18A.

I think it will be a several more weeks before I have finalised the mini-cortex design and tested the circuit on the bread board: as-is it is not a 'confirmed working' schematic, let alone a confirmed working PCB.
 
ROM images for the Tutor are widely available. What is not well-understood is how the banking logic in the CLA works, and there are some locations at >EExx that do "magic" no one has fully documented yet.
 
Hello friends, i am a TI99 user.. i looked last summer a real powertran cortex and looked that is more near at my computer. i start at use the emulator and i wont try at learn a basic.. now i have a problem.. i used emulator v2.0, and i load a dump disk image with a basic program.. exist a mode for print a listate or extract the file in ascii mode for read it and print? I no have a real powertran in Italy is more rarest :)
thanks Ermanno
 
ti99/4a said:
I'm looking for a supplier to make some double sided PCBs.. does anyone know or can recommend a reputable company ?

I've been told that you can get a good quality 300mm x 160mm Double sided board for £15 each, though you have to order min 10 boards !
Click to expand...

Ksarul put me onto www.sitopway.com, who I've used three times now, and couldn't be happier. Have ordered the boards with green soldermask and white silkscreen. Turnaround is 5 days. No minimum quantity as far as I'm aware - I've only ordered around 3 of each board.

No online quote tool like some of the other PCB manufacturers, but send a copy of the gerbers plus spec and quantity you need to [sales@sitopway.com] and they'll get back to you with a quote within 24 hours or so. For both the orders I've placed, have also received an extra 1 or 2 of the boards free. Not sure if that's just a teaser for a new customer, or extras they managed to squeeze onto the larger manufacturing panel.

Stuart.
 
You must log in or register to reply here.
Back
Top