Max number of side car addons

[Chuckphd53]

I am sure this has been answered, I did a quick google search, nothing,,,

How many side car add ons did IBM spec was the limit.
I understand it depends on the design and power consumption, but was there a Rule Of thumb from IBM on this subject...
My quest is the Data and Address Control line Fan out /signal propagation degradation.

so, Given that the original platform may only have Memory/LPT/Speech/ any others?? without the add on power adapter.
Understanding that some of them may have their own power supply.

Again just looking for number that IBM thought would be the max...

[Trixter]

Officially, this is a question for Mike. I can say that I've put 3 memory sidecars, LPT sidecar, power sidecar, and a speech sidecar on a single system without issues. You are probably fine with any number of sidecars as long as there are no resource conflicts and every 4th sidecar is a power sidecar.

[Chuckphd53]

I am trying to understand what I mentioned in another thread.
that is:
using the JRIDE and ParPort side car

Experiment.
I have set up two Jr's 'stock'.
on both systems, when I install the JRIDE first, then the ParPort on the outside position
the JR will boot and all is good.....now there are times that the ParPort does not get found by the system and I have to reboot
but I have not resolved this to be the order of install, but it does fall in line with the experiment.

on both systems, when I install the ParPort first, then the JRIDE on the outside position
the JR will not boot, gets to the JRIDE ROM display and sometimes ESC prompt
but at that point Freezes.... Power down is the only remedy..

Now I did ( as mentioned in other thread) after reviewing the JR desgin, add PULLUP/PULLDOWN Termination resistors 390UP /470DWN
and put these on the D0-D7 lines, now the system will boot reliably in any combination.

so this gets me to this Thread, and the number of addon's that seem to work ok....
The JRIDE has 6 fanout paths for the D0-D7 lines to the RAM / Flash / CPLDs / RTC.
I suspect that the loading is typically at the limit the Jr's LS245 can drive, hence the PULLUP/PULLDOWN
assist in the signal transition and this allow proper operation...

ON the JRIDE I layed out, on the board I put these resistors down and the board works fine
also in either position...

I suspect that IBM never envisioned the JR Folks going crazy on the side cars other than a few
which as you mentioned Jim, works fine....

Anyway, I am on a quest to fully understand this, Scope in hand will solve this in the coming weeks...

Also if anyone else is using the JRIDE and ParPort side cars together I would like to hear your experience
on Postion of the side cars and how the operation on your system...

Chuck

[alanh]

Just some historical context, the JR-IDE project was designed quickly and without much thought to stacking a lot of side-cars along with it as it fulfills most needs. I should have added a '245 for data but it wasn't a big concern at the time.

[Chuckphd53]

Yea not a big deal as most folks dont see this issue. it may just be me

I would like to solve this incase it does rear its ugly head up...if at all...

[Trixter]

I've only used my jrIDE with an LPT sidecar and both have worked just fine. I believe my jrIDE is the last sidecar.

[Chuckphd53]

That is good news, In that config both my systems would hang with that config...
I upgraded, a JRIDE today with the PULLUP/DOWN and now that board will boot fully on both machines.j
I may have a couple earlier boards and my mileage is just a fluke, hopefully....

[Chuckphd53]

The earlier boards meaning PCJr systems.
But I would be interested in anyone else with this setup also...

[FortMax]

I'm having the same problem, except I have a rapport Drive 2 and jrIDE. Nothing else.
Most of the time, I get two short beeps and a black screen when I power the PCjr on.
If I have the jrIDE between the PCjr and Rapport sidecar, which isn't ideal, it boots every time

[Chuckphd53]

Here is a very Crude quick cheap fix for the original JRIDE boards if you
are having issues with them in the OUTSIDE POSITION of the sidecar order...

note that the Resistors are layed flat to the board so they do not touch the inside of the case when put back together.
also try to keep the resistors a little 'off' the board when you are done...
If you feel like you want to put some Kapton Tap down first that is a good idea as an isulation layer, not needed if you are careful.

The pins to attach to are marked with a YELLOW Circle
and the 5V+ and GND are also noted.

Review the pictures to be sure you get all the connections correctly placed..

hope this helps those that may have an issue.... if it does please report back with your results..
Chuck