+- Discussion Forum for all things Microbee (https://microbeetechnology.com.au/forum)
+-- Forum: Microbee Forum (https://microbeetechnology.com.au/forum/forum-1.html)
+--- Forum: Microbee Hardware (https://microbeetechnology.com.au/forum/forum-6.html)
+--- Thread: Upgrading the original ROMs in a 32KB Microbee (/thread-260.html)
RE: Upgrading the original ROMs in a 32KB Microbee - g67wjjk - 12-01-2021
Ahhhh, okay, good to know. I never saw a blinking * ...
Yeah, I'll convert them to mono, choosing the best looking channel in Audacity, and have a go ... I'll stick with Turtle to start with. And I'll definitely try the Monitor trick, thanks.
I realised that I had Dolby-B NR active on all the recordings, duh. Want me to try the PRIMUG Side A again with NR off to see if that helps? When looking in Audacity, it does look like there's different recording levels in the new tapes - I'm using a Yamaha component tape deck with line-out and the recorder input set to line-in so that shouldn't be an issue.
RE: Upgrading the original ROMs in a 32KB Microbee - ChickenMan - 12-01-2021
The * more turns on and off rather than blink. The underline/cursor should blink on & off though as soon as you type in LOAD and hit Return.
Yes another recording of Primug Side A with NR turned off would be good, thanks.
RE: Upgrading the original ROMs in a 32KB Microbee - someone - 12-01-2021
One hassle for diagnosing tape read problems with a microbee is that it is time critically bit bashed and its standard ROM TAPE read routines don't provide a real time bit received display capability.
The microbee's predecessor - DGZ80 has a wonderful inbuilt tape bit detector. Rather than the alternating '*' between each successfully received block, the DGOS tape routines used an animated chunky graphics character to show tape data activity through out the block read. The DGZ80 could do this because it's cassette interface was partially hardware driven, software bit bashed, had no video deglitching circuit and had a bit of spare time to do so (@300 baud).
The method used to calibrate the DGZ80's cassette interface (USCI and SECI) was use the DGOS monitor to:
1. Fill the screen up with 'U's (i.e. binary code 01010101)
>F F000 F3FF 55
2. Write a test tape using
>W "TEST" T F000 F3FF
3. and then read it back using
>R
The screen would read the header and in real time you could see the screen fill up with 'U's if everything was working. If it wasn't junk characters or flashing a 'C' for CRC errors would appear.
(12-01-2021, 05:38 PM)g67wjjk Wrote:(12-01-2021, 08:03 AM)someone Wrote: Do you ever sleep?
23 years with Nokia ... 20 years, and counting, on emergency call-up in various countries. Used to working weird hours ... people get pissy/whine to Whirlpool when they can't use their phone
Is that Nokia, Microsoft or both?
Pissy? Someone was forced to transition from Bigpond Cable to the NBN back in September and lost their phone number in the process. Telstra didn't port the phone number as requested. It's some 3 months later and Telstra still hasn't completed the job to get it back even with an official TIO Complaint (Telecommunications Industry Ombudsman). The latest communique with the TIO stipulated that they've been inundated with issues and have a 5 week lag time. Someone knows of a poor restaurant that's had a similar issue with their customers thinking that they've closed down because they can't be contacted. How horrible for the restaurant owners and staff!!
RE: Upgrading the original ROMs in a 32KB Microbee - g67wjjk - 13-01-2021
The 8Ω speakers I initially ordered from Element 14 arrived today, in their usual & efficient manner.
But I'm wondering whether they are actually the correct impedance for my 32.
I've been comparing the schematics of the two early main boards - the initial 'Bees had 8Ω speakers before switching to 50Ω.
The audio part of my 'Bee looks like the earlier 8Ω speaker circuit ... R27 is a big, beefy ... 1/2W? ... 27Ω resistor ... and not a 220Ω resistor in the 50Ω speaker circuit.
I decided to use a detachable cable to make it easy to remove the main board without having to unscrew the speaker.
From the marks on the speaker grill, this is the one that had the unknown-impedance speaker jammed in upside-down and then glued to the speaker grill, whereas the one I have that is clearly marked 50Ω is from a Series 2 Educator I have. I'm working on both at the same time.
RE: Upgrading the original ROMs in a 32KB Microbee - g67wjjk - 14-01-2021
(03-01-2021, 04:52 PM)ChickenMan Wrote: If your Eprom burner can handle 2732, you just need to make up an adapter to allow it to burn 2532's, which is what did, and its all explained here - https://atariage.com/forums/topic/269633-replacing-a-tms2532-with-a-2732/ or here http://www.thegleek.com/bobroberts/mspacrom.html
I'm going to give that a go. I've got a Wellon VP598 - will make up an adaptor and then I just need to choose a 2732 and modify Vpp from 21V to 25V.
Alternatively, as the documentation describes how to modify the NET socket from 2532 to 2732, couldn't similar be done for the other ROM sockets?
Although, I do have more 2532s than 2732s (i.e. original BASIC ROMs I could erase/update) ...
RE: Upgrading the original ROMs in a 32KB Microbee - g67wjjk - 22-01-2021
Okay, I've run into a snag with this machine.
I did four modifications at once before testing, always a no-no when testing/troubleshooting - two on the main board and two on the core board. I'm confident the main board is fine (RS232 improvements) as they look similar to a Series 2 and it also "works" with a Series 2 core board (beeps and has video output, but doesn't work properly because it's 2MHz but BASIC 5.22 on the core board I assume).
The modifications on the core board were:
[1] I modified the NET IC34 as per the HWNB from 2532 to 2732 but it didn't work - and the instructions didn't make much sense in hindsight so I did something else. I drilled out the holes, cut tracks, soldered in a socket and C31.
The HWNB (section B, chapter 6) details how to modify the socket to accept a 2732 - it says to connect pin 21 (A11) to pin 18 of IC25 - simple enough. It then says to connect pin 18 (enable) to pin 1 of IC26 (A12 line).
This confused me - shouldn't the 2732 ENABLE connect to the ROMSEL line - the 2532 pin 20 connects to IC26 pin 9 ... not pin 1. So I moved pin 18 to pin 9.
Summary: the NET ROM (IC34) now has pin 21 (was PD/PGM, now A11) connected to A11, and pin 18 (was A11, now ENABLE) connected to ROMSEL, and not A12.
[2] I added the missing components for the battery backup according to the schematic: R5, R6, R9, R12, TR1, LED.
I'm feeling that the NET ROM is causing the issue - voltages look fine, will hook up a logic analyser next. I'm assuming it should still work without the BB connected?
But in case someone has an idea where I went wrong
RE: Upgrading the original ROMs in a 32KB Microbee - Ernest - 22-01-2021
To change the NET ROM from 2532 to a 2732 on the MB1632 version 1 board, then all you should need to
a) Disconnect PIN 18 from A11 line and jumper PIN 18 to Pin 20.
b) Disconnect Pin 21 from the +5V rail and connect to the A11 Line.
Don't change anything with the !ROMSEL line unless you wish to change which ROM you boot too.
You need to keep it where it is to boot from BASIC.
If you want to do away with BASIC and Boot from the NET ROM position, you need to have a ROM there that is Bootable
I.E. Boot ROM for Disk system BN56.
If you have a later version of the MB1632 then the change is even easier. Look at the schematic for the MB1656.
1) Cut links E-F, A-B
2) Link E-D, B-C
Ernest
On the Battery Backup side, that is only needed to maintain selection and Memory in the SRAM during power down, som the system returns to where it was before power down. The system will work normally otherwise even without these parts. If in doubt with what you have fitted then lift one end of D4 to separate this circuit from the rest of the system.
Ernest
RE: Upgrading the original ROMs in a 32KB Microbee - someone - 23-01-2021
The /ROMSEL signal is used to enable the Z80 to access the system data bus.
After a reset, the system data bus is isolated from the Z80 CPU and with the pulldown resistor pack on the CPU's data pins presenting a %00 NOP instruction to it so the address bus continually increments until the /ROMSEL is asserted usually by a ROM's /CS (or equivalent) signal (which has been asserted by the address presented on the address bus along with the appropriate control signals such as /MREQ). So with that explained, for MWBASIC, the /ROMSEL is connected to the /CS of the first MWBASIC ROM at address %8000, on a 56K coreboard /ROMSEL is asserted by the /CS of the Boot ROM at address %E000.
#NOTE: ROM assertion is a combination of /CS and /OE. In some designs the /CS is tied low making the /OE being the assertion mechanism, some vice versa and others employing more complicated schemes.
On a DRAM coreboard it works a similarly but with the /NMI signal used in place of the /RESET signal and a short pulse generator to assert the Z80 CPU' s isolation from the data bus.
This was done as a measure to ensure that the Dynamic RAMs would be continually refreshed. If the /RESET signal was used, the DRAM /RFSH signal that refreshes the DRAM would temporarily stop risking the DRAMs from being refreshed and data being lost.
A DRAM coreboard boots up at %8000 allowing it to boot up as a MWBASIC coreboard with ROMS at %8000-%EFFF and RAM at %0000-7FFF or more normally booting up a DRAM coreboard boot ROM (at %8000) such as BN54 that configures the system to emulate a 56K coreboard system with a BIOS at %E000 and RAM at %0000-DFFF.
On a 128K DRAM coreboard, amongst other things, the DRAM is presented as 4 pages of 32K with all pages being presentable at memory address %0000-7FFF and only one at %8000-%FFFF. Upon an /NMI the memory is reset to is default configuration of DRAM at %0000-7FFF (unintuitively page #1 and not #0) and Boot ROM at %8000.
2532-to-2732 ROM adaptors - g67wjjk - 03-05-2021
My 2532-to-2732 adaptors *finally* arrived!
Ordered Feb 1st, shipped Feb 6th ... arrived in Sydney Apr 28th, delivered to Port May 3rd. Okay, they did quote 30-60 days ... and I only paid US$5 for ten boards with US$7 shipping ... whereas normally I'd be charged US$30 "remote area fee" on top of normal "express" shipping. So pretty good value.
Now to get my Microbee 32 back to a state where I can test it - I've got 13.5MHz crystals now so I can attempt upgrading it, including the BASIC.
/Brett