Re: TRS-80 Model 1 Expansion Interface question?

[Eric Smith via cctalk]

On Mon, Mar 20, 2017 at 6:46 PM, Win Heagy via cctech  wrote:

> The expansion interface hardware manual indicates
> it is an FD1771B-01, but the service manual indicates a couple
> possibilitiesFD1771 A/B -01 -11.  Any considerations to look for here?
>

All other things being equal, I'd use the FD1771x-01, with x being either A
or B.

The A vs. B is just whether the chip is in a ceramic (A) or plastic (B)
package. This makes no difference in the TRS-80 EI.

The numeric suffix indicates functional or specification differences.
The -01 suffix is rated for operation at 1 MHz or 2 MHz, which is fine for
the TRS-80 EI, which runs it at 1 MHz (as required for 5.25-inch
standard-density floppies).
The -02 suffix is rated for operation at 2 MHz only, so in principle it
isn't guaranteed to work in the TRS-80 EI, but in practice it should work
fine.
The -11 suffix is for a part that has an internal substrate bias generator,
so pin 1 (Vbb) should be disconnected. This wouldn't meet spec in the
TRS-80 EI without disconnecting pin 1, though it's possible that it might
work OK without doing so.

At 1 MHz, the available stepping rate selections for the -01 and -11 are
12, 20, and 40 ms, while for the -02 they are 12, 16, and 20 ms.

Re: TRS-80 Model 1 Expansion Interface question?

[Fred Cisin via cctalk]

On Mon, 20 Mar 2017, Win Heagy via cctech wrote:

But, the FD1771 IC, for some reason, was removed from an otherwise
apparently functional EI.
http://imgur.com/a/3NzOh
Is there any reason why this chip would be removed?  I see a number of them
on ebay for around $25.  The expansion interface hardware manual indicates
it is an FD1771B-01, but the service manual indicates a couple
possibilitiesFD1771 A/B -01 -11.  Any considerations to look for here?



Some owners replaced the 1771 with a daughterboard that contained a 1771 
plus a better data separation circuit.  The 1771 included internal data 
separation, which WD advised not to use.

"EVERYBODY" used one of those.
Before selling the Expansion Interface, the previous owner might have 
removed the data separator and sold it separately.


Some owners replaced the 1771 with a daughterboard that contained a 1771 
plus a 179x, called a "Doubler".  That added double density (MFM) support. 
The Doubler included a 1771 because the 179x was incapable of writing some 
of the address marks that Model 1 TRSDOS used in its disk format.

"EVERYBODY" used one of those.
Before selling the Expansion Interface, the previous owner might have 
removed the Doubler and sold it separately.


Both the Data Separator and the Doubler COULD HAVE used the 1771 that was 
taken out, but usually came with one already installed.
1) it made for one less prying out, bending pins and reinstalling with 
bent pins or backwards

2) it meant that there was a known good chip going in.


Some owners replaced the 1771 with an aftermarket daughterboard that 
contained a 1771 plus some circuitry to do 8" SSSD.  Often that was 
accompanied by a sandwich board for the Z80 in the CPU to remap memory for 
CP/M, and a CP/M for it.

(such as Parasitic Engineering, and Omikron Mapper)
"not EVERYBODY" used one of those.
Before selling the Expansion Interface, the previous owner might have 
removed the adapter and sold it separately.
(There also existed a "remapped" CP/M for the TRS80 that would work 
without the hardware remapping, although in general no known 
commercial software worked with that setup.)




In addition to the 1771, does your Expansion Interface include the "RS232 
board"?  A Radio Shack Computer Store manager asserted that any 
incompatabilities with the standard were legitimate, "because OUR RS-232 
board is RADIO SHACK 232"
Before selling the Expansion Interface, the previous owner might have 
removed the adapter and sold it separately.



There were a few modifications to the EI over time.
The first version had a simple straight through cable.
Then they made some changes and switched to a cable with a circuit box in 
the middle of it.
Then they made some changes and switched to a cable with a circuit box in 
the middle of it, plus a small second cable.
Then they made some changes and switched to a simple straight through 
cable.
Make sure that you use the appropriate cable(s) for the level of changes 
that were made to yours.


To keep reliability, do not plug/unplug and move the CPU and the EI.
If you are going to do so, then bolt both pieces to a piece of plywood. 
RIV-NUTS or NUTSERTS into holes drilled into the bottom of the EI and CPU.



You did not HAVE TO put the power supply for the CPU into the compartment 
in the EI.  If you do, cutting a notch in the case means that you can tuck 
the excess cord in there to have 3" of power cord between the EI and CPU, 
instead of a couple of feet going out the BACK and around to the front.



The RCA TV set that Radio Shack used as a monitor had a great big empty 
space where the tuner used to be.  Plenty of room for a disk drive, or a 
pair of half-height drives.  Mu-metal surround was kinda important.


The CPU needed a trivial modification to add lower-case.  Often 
accompanied by adding a "Control key", and sometimes a mod to give reverse 
video.  Remember to put glyptol on the screw after making modifications, 
since warranty was void if there wasn't any glyptol.



--
Grumpy Ol' Fred ci...@xenosoft.com

Re: TRS-80 Model 1 Expansion Interface question?

[Fred Cisin via cctalk]

On Mon, 20 Mar 2017, ben via cctech wrote:

Act quick before Radio Shack closes its doors forever.


Radio Shack stores haven't had any of that stuff for decades.


One Doubler on eBay; no 1771s

Re: TRS-80 Model 1 Expansion Interface question?

[ben via cctalk]

On 3/20/2017 9:43 PM, Fred Cisin via cctech wrote:

On Mon, 20 Mar 2017, Win Heagy via cctech wrote:

But, the FD1771 IC, for some reason, was removed from an otherwise
apparently functional EI.
http://imgur.com/a/3NzOh
Is there any reason why this chip would be removed?  I see a number of
them
on ebay for around $25.  The expansion interface hardware manual
indicates
it is an FD1771B-01, but the service manual indicates a couple
possibilitiesFD1771 A/B -01 -11.  Any considerations to look for
here?



Some owners replaced the 1771 with a daughterboard that contained a 1771
plus a better data separation circuit.  The 1771 included internal data
separation, which WD advised not to use.
"EVERYBODY" used one of those.
Before selling the Expansion Interface, the previous owner might have
removed the data separator and sold it separately.

Some owners replaced the 1771 with a daughterboard that contained a 1771
plus a 179x, called a "Doubler".  That added double density (MFM)
support. The Doubler included a 1771 because the 179x was incapable of
writing some of the address marks that Model 1 TRSDOS used in its disk
format.
"EVERYBODY" used one of those.
Before selling the Expansion Interface, the previous owner might have
removed the Doubler and sold it separately.

Both the Data Separator and the Doubler COULD HAVE used the 1771 that
was taken out, but usually came with one already installed.
1) it made for one less prying out, bending pins and reinstalling with
bent pins or backwards
2) it meant that there was a known good chip going in.


Some owners replaced the 1771 with an aftermarket daughterboard that
contained a 1771 plus some circuitry to do 8" SSSD.  Often that was
accompanied by a sandwich board for the Z80 in the CPU to remap memory
for CP/M, and a CP/M for it.
(such as Parasitic Engineering, and Omikron Mapper)
"not EVERYBODY" used one of those.
Before selling the Expansion Interface, the previous owner might have
removed the adapter and sold it separately.
(There also existed a "remapped" CP/M for the TRS80 that would work
without the hardware remapping, although in general no known commercial
software worked with that setup.)



In addition to the 1771, does your Expansion Interface include the
"RS232 board"?  A Radio Shack Computer Store manager asserted that any
incompatabilities with the standard were legitimate, "because OUR RS-232
board is RADIO SHACK 232"
Before selling the Expansion Interface, the previous owner might have
removed the adapter and sold it separately.


There were a few modifications to the EI over time.
The first version had a simple straight through cable.
Then they made some changes and switched to a cable with a circuit box
in the middle of it.
Then they made some changes and switched to a cable with a circuit box
in the middle of it, plus a small second cable.
Then they made some changes and switched to a simple straight through
cable.
Make sure that you use the appropriate cable(s) for the level of changes
that were made to yours.

To keep reliability, do not plug/unplug and move the CPU and the EI.
If you are going to do so, then bolt both pieces to a piece of plywood.
RIV-NUTS or NUTSERTS into holes drilled into the bottom of the EI and CPU.


You did not HAVE TO put the power supply for the CPU into the
compartment in the EI.  If you do, cutting a notch in the case means
that you can tuck the excess cord in there to have 3" of power cord
between the EI and CPU, instead of a couple of feet going out the BACK
and around to the front.


The RCA TV set that Radio Shack used as a monitor had a great big empty
space where the tuner used to be.  Plenty of room for a disk drive, or a
pair of half-height drives.  Mu-metal surround was kinda important.

The CPU needed a trivial modification to add lower-case.  Often
accompanied by adding a "Control key", and sometimes a mod to give
reverse video.  Remember to put glyptol on the screw after making
modifications, since warranty was void if there wasn't any glyptol.


Act quick before Radio Shack closes its doors forever.



--
Grumpy Ol' Fred ci...@xenosoft.com


Ben.
What happens to my life tube replacement guarantee now?

Re: TRS-80 Model 1 Expansion Interface question?

[Peter Cetinski via cctalk]

> On Mar 20, 2017, at 8:46 PM, Win Heagy via cctech  
> wrote:
> 
> Is there any reason why this chip would be removed?  I see a number of them
> on ebay for around $25.  The expansion interface hardware manual indicates
> it is an FD1771B-01, but the service manual indicates a couple
> possibilitiesFD1771 A/B -01 -11.  Any considerations to look for here?
> 

The EI may have had a double density board which plugs into the FDC chip 
socket.  The FDC chip then plugs into the doubler.  Without the doubler you 
only have single density.  Original Percom or Tandy doublers are fairly rare to 
find today so someone may have pulled it out to sell.  Ian Mavric in Australia 
does make reproductions though.

TRS-80 Model 1 Expansion Interface question?

[Win Heagy via cctalk]

I have a clean, and somewhat functional expansion interface that I just
tested over the weekend.  Without the EI connected, the model 1 reports
~16K RAM and with the EI the model 1 reports ~48K, so the RAM seems OK.
But, the FD1771 IC, for some reason, was removed from an otherwise
apparently functional EI.
http://imgur.com/a/3NzOh

Is there any reason why this chip would be removed?  I see a number of them
on ebay for around $25.  The expansion interface hardware manual indicates
it is an FD1771B-01, but the service manual indicates a couple
possibilitiesFD1771 A/B -01 -11.  Any considerations to look for here?

Thanks,

Win