Hi Lew,
Nice collection you have there
"Number 3 is a B-ETI Serial Terminal. I have found this morning that it does seem to work, but seems to be sensitive to supply voltage, and only seems to boot up when I change that (between about 10 and 12 V DC). This might just be a capacitor issue. I'm not sure how much use a maximum 4800 baud terminal would be these days - it's seems so much easier to use a program on a PC. Maybe this unit could be reprogrammed as a Microbee?"
Haven't seen one of these in a very long time. The unique aspect of this terminal was it's ability to be used for the old Baudot RTTY as was common in the day among radio Amature's as the old Teleprinters that were cheep to pickups from disposal stores in the early eighties became more and more rare.
As you have a couple of the normal MB1248 Mainboards on your other machines, if you are going to make the change to the B-ETI, I would look at doing any changes as a two step approach.
1) Do the Coreboard first and get it working on one of your other MB1248's.
2) Then look at tackling the Mainboard.
The great advantage you have is having a number of systems to work with.
The Coreboard should be straight forward (just missing quite a number of parts) as only 2K of SRAM was fitted to those units, this was in the memory space of D800h - DFFFh .
As most of the board is empty, this would give you a reasonably blank canvas to work with, I would look at fitting a 256K SRAM single chip to give you a 32K unit with minimal changes.
If my understanding of the B-ETI is correct, the Mainboard also had differences from the normal Microbee.
It didn't have the PGC RAM or supporting chips and also I think IC16 the Bipolar PROM 82S123 was different, most likely all to do with the lack of PGC RAM.
As there was no program memory as such, they also omitted the cassette interface parts around and including IC35 (nowhere to load a program too anyway).
Enjoy your exploration.
Ernest
Nice collection you have there
"Number 3 is a B-ETI Serial Terminal. I have found this morning that it does seem to work, but seems to be sensitive to supply voltage, and only seems to boot up when I change that (between about 10 and 12 V DC). This might just be a capacitor issue. I'm not sure how much use a maximum 4800 baud terminal would be these days - it's seems so much easier to use a program on a PC. Maybe this unit could be reprogrammed as a Microbee?"
Haven't seen one of these in a very long time. The unique aspect of this terminal was it's ability to be used for the old Baudot RTTY as was common in the day among radio Amature's as the old Teleprinters that were cheep to pickups from disposal stores in the early eighties became more and more rare.
As you have a couple of the normal MB1248 Mainboards on your other machines, if you are going to make the change to the B-ETI, I would look at doing any changes as a two step approach.
1) Do the Coreboard first and get it working on one of your other MB1248's.
2) Then look at tackling the Mainboard.
The great advantage you have is having a number of systems to work with.
The Coreboard should be straight forward (just missing quite a number of parts) as only 2K of SRAM was fitted to those units, this was in the memory space of D800h - DFFFh .
As most of the board is empty, this would give you a reasonably blank canvas to work with, I would look at fitting a 256K SRAM single chip to give you a 32K unit with minimal changes.
If my understanding of the B-ETI is correct, the Mainboard also had differences from the normal Microbee.
It didn't have the PGC RAM or supporting chips and also I think IC16 the Bipolar PROM 82S123 was different, most likely all to do with the lack of PGC RAM.
As there was no program memory as such, they also omitted the cassette interface parts around and including IC35 (nowhere to load a program too anyway).
Enjoy your exploration.
Ernest