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+--- Thread: Upgrading the original ROMs in a 32KB Microbee (/thread-260.html)
RE: Upgrading the original ROMs in a 32KB Microbee - someone - 09-01-2021
(08-01-2021, 10:32 PM)Ernest Wrote: Hi someone,Thanks Ernest,
Check out the PCF emulation in the uBee512 documentation.
It is a compilation all in one 256K ROM, able to emulate the PC85 as well as being able to boot from an IDE drive.
Leaving out the boot portion, a full PC85 should run all from the one ROM.
I'm guessing that this is what CM has on his Coreboard.
Ernest
You've got great eyes for being to decipher that from the lores photo.
It just looks like a smudge to me.
Without any other bells and whistles on that coreboard I've guessed the ROM would of just contained MWB and concatenated with maybe EDASM/WORDBEE and a NETROM.
RE: Upgrading the original ROMs in a 32KB Microbee - g67wjjk - 09-01-2021
Thanks everyone for your advice. I think I'll just offer this one as is, after some repairs to ensure it's working nicely and the computer is clean. But I could do some of those simple modifications detailed in the HW NB.
The HW NB also mentions about modifying the NETWORK socket to accept a 2732, noting that Pascal could be used?
RE: Upgrading the original ROMs in a 32KB Microbee - g67wjjk - 11-01-2021
Okay, I've identified the modifications I should do on this Microbee 32:
[1] Revised cassette interface
[2] Removing white flickers - ground pin 4 of IC16
[3] Stopping noise on the RS232 RXD line - add 18kΩ resistor
[4] RS232 output circuit TXD - change 3.3kΩ to 18kΩ
[5] Modify NET ROM from 2532 to 2732 and add Pascal (if I have a 2732 handy)
For [1], it says to move C23 to TP8/9 ... I don't see any TPs labelled on the board ... can I just put it in parallel with R24?
Going to skip the 13.5MHz and dual font ROM changes.
RE: Upgrading the original ROMs in a 32KB Microbee - Ernest - 11-01-2021
Hi Brett,
If you have it set up as per the MOD diagram above I.E. R23 = 10K, R24 = 1.5K & C23 = 100nF then you will have it set to what was the most recent revision of the MB1248 Mainboard.
I think your current configuration has the capacitor in series with the cassette output.
Ernest
RE: Upgrading the original ROMs in a 32KB Microbee - g67wjjk - 11-01-2021
Currently R23 = 3.3kΩ, R24=470Ω and C23=100nF.
So I need to replace the resistors with new values, remove C23 totally and replace with a link, then put a new 10nF C23 in parallel with R24 ... so was just thinking of just putting it on top of R24, or underneath. When I looked at my other two Mainboards, they have specified TPs on the board.
RE: Upgrading the original ROMs in a 32KB Microbee - someone - 11-01-2021
Someone wouldn't have touched the cassette interface components unless constant experiencing problems.
For the output section its performance is dictated by many factors of the accompanying cassette recorder such as its input impedance and its input gain section.
For example, many mic inputs are high impedance and high gain and line inputs are low impedance and low gain.
RE: Upgrading the original ROMs in a 32KB Microbee - g67wjjk - 12-01-2021
(11-01-2021, 07:35 PM)someone Wrote: Someone wouldn't have touched the cassette interface components unless constant experiencing problems.
For the output section its performance is dictated by many factors of the accompanying cassette recorder such as its input impedance and its input gain section.
For example, many mic inputs are high impedance and high gain and line inputs are low impedance and low gain.
Ahh. Well I didn't have any luck when trying to load WAV samples from a digital recorder. Same ones that I made for CM. So I thought maybe that would help.
It could read the header, I assume ... I would try load"" or load"turtle" ... I would see it print TURTLE M ... then nothing as the WAV file finished. I eventually realised that the last character meant B for BASIC and M for machine code.
So if it could read the filename at the volume I set, then I assume it should've been able to read the rest of the sample. I did try various volume settings on the digital recorder.
Of course, I could be using the entirely wrong command to load - I didn't bother reading the manual.
Okay, command should be okay ... it says I can used LOAD? to also verify checksums, so maybe I'll try that too.
I did make an LPF I'd read about that included a speaker - I might try hooking that up - I'm guessing it was remove 50Hz hum from the tape player or something?
Reading further ... ouch, harsh!
This option should only be used as a desperation measure when you have been foolish enough not to dump two copies when SAVEing and then verify the first one.
RE: Upgrading the original ROMs in a 32KB Microbee - someone - 12-01-2021
Do you ever sleep?
Which inputs are your using on your digital recorder? Someone uses a Roland Sonar V-STUDIO 100 and a Micron Tape recorder with no probs once the optimal volume settings were determined. The V-STUDIO 100 specs are a little overboard.
The microbee's cassette interface is just a couple of bit bashed I/O bits and seeing if it works properly is a relative doddle.
Do you have an oscilloscope or equivalent by any chance?
It does make fixing these things much easier.
If not, you can use a .wav waveform viewer to spot any anomalies on the recording.
For checking the input circuit, i.e. the CA3140 you can use something like a USB oscilloscope or equivalent to record the incoming bitstream.
The Digilent Analog Discovery is handy for the recording but any equivalent will do (e.g. Red Pitaya, POScope). They're just like a 21st Century Microbees! Fun Gadgets!!
RE: Upgrading the original ROMs in a 32KB Microbee - g67wjjk - 12-01-2021
I was using a Sony ICD-PX470, same one I used to digitise the tapes for CM - I just tried the same file that CM used successfully, 16-bit 44.1kHz. So simple headphone output. Although, stereo output but using the mono plug into the 'Bee ... but that would just ground the other channel ... ? But I could try picking a channel and converting it to mono.
And I can also trying saving a file from the 'Bee to see what that WAV file looks like.
I have tried copying mono WAV files across (i.e. for ZX81) but the Sony was a real pain trying to get it to recognise the file as it's quite simple I think, only expecting 16-bit/44.1kHz. So I switched to playing them from my laptop and it worked.
I've got other means - DAT recorders, Hi-MD MiniDisc recorders (in LPCM format), actual tape recorders ... or even just use my laptop.
I do have an oscilloscope, and also a logic analyser - so I could hook them up to see what's actually happening. Will try that.
Once it has identified the file name ... i.e. prints TURTLE M ... should it print anything else to indicating it's loading, etc.? I don't see anything.
RE: Upgrading the original ROMs in a 32KB Microbee - ChickenMan - 12-01-2021
Of your recordings, TURTLE was the only one that would load error free straight off. But I did remove one channel first and save as a MONO file then loaded that. Most of the other files I have not been able to get an error free load at all. Side B of the PRIMUG loads okay, but not A.
When a tape loads in, TURTLE for example, you get to screen after entering LOAD and hitting Return
TURTLE M *
with the * coming on and off for a few seconds each time as the tape loads. B = Basic, M = Machine code, W = Wordbee & S = Source (from EDASM). Turtle is actually a Basic file but its been assigned here as a Machine code because then an Auto Start address can be assigned and it the program auto starts once loaded. Otherwise, you have to type in RUN.
Also to see better whats going on when a tape loads, jump to the Monitor (hold down M & Reset for a few secs and release Reset), the type in R & hit Return and start the tape player. You again will see TURTLE M but now also its load address, auto start address and file length all in Hex. and a countdown of its length as it loads in till it reaches zero. From the Monitor, it will not auto start as it just Loads. So now at the cursor, and being a BASIC program, just type G 801E and hit Return. G = Goto and 801E is the Auto start address of a Basic program.