25-01-2022, 02:54 PM
(This post was last modified: 26-01-2022, 11:21 PM by someone.
Edit Reason: Clarify some details.
)
G'Day Chesh,
Why not make this an opportunity to make your own Expansion board that connects to an early Microbee32 using its 50 way connector?
These days its really easy to do.
Someone hopes you enjoy this post.
As a guide, attached below are the modifications to a MWB1732 coreboard to work with the prototype Microbee Cartridge Expansion slot.
(As it panned out, RAMs of a suitable size for the cartridges did not become available in time nor at a satisfactory price. Also, that the original intention was to increase the CPU speed to 4MHz but this was not done due to the expense of faster ROMS.)
[#NOTE: There ware performance issues with the MASK FONT ROMS produced by Texas Instruments even working at 3.375MHz. It is preferable to burn your own with faster EPROMS].
1. /PHANTOM SIGNAL ADJUSTMENT
This makes the /PHANTOM signal effective only for coreboard ROMS at memory address %8000-EFFF.
Reconfigure the /PHANTOM signal by disconnecting it from IC20, pin 6 and connecting it to IC22, pin 6.
2. /ROMSEL SIGNAL ADJUSTMENT
This makes the /ROMSEL signal switch between coreboard MWB ROM A to the a signal on the 50 way expansion connector.
Connect the /ROMSEL to pin 10 on the 50 Way Expansion connector (i.e. reallocated from Z80 /HALT).
Cut PCB track from /ROMSEL to IC22 pin 11 then insert series resistor between IC22 pin 11 and ROMSEL.
3.*Only for 2MHz: CRYSTAL ADJUSTMENT
This provides the CRTC with a dot clock capable of displaying 80*25 characters.
Change the onboard 12MHZ crystal with a 13.5MHz crystal.
On the Motherboard, disconnect the CPU Clock from the 74LS92 divide by 6 output and connect to the divide by 4 dot clock output on the 74LS161.
4.*Only for 2MHz Systems: MWB ROM UPDATE
Replace MWB ROMS with 3.375MHz compatible version.
This version of BASIC is reconfigured to handle the increased CRTC Dot Clock and increased CPU clock speed.
The speaker pitches and durations have been adjusted sound correct.
5.*Only for 2MHz Systems: DUAL FONT ROM UPGRADE
This enables the microbee to display a font suitable for 80x24 character resolution.
Description
The Cartridge Expansion port enables a microbee 32K to work with plug in ROM and RAM expansion cartridges enabling it to work with disk drives and CP/M and work with extended play Game Play cartridges. Rather than waiting an eternity for a tape to load, ROM Cartridge based games are loaded instantly.
Theory of operation
When the cartridge port is disconnected, the microbee behaves as normal.
When the cartridge port is connected with no cartridge inserted, the microbee behaves as normal.
When the cartridge port is connected and a cartridge is inserted to the cartridge slot , the ROMs on the coreboard are disabled being replaced with the memory decoded by the inserted cartridge.
This memory can either RAM, ROM or a combination of both.
The /ROMSEL signal is connected to the memory address decoding output of the desired boot address.
For the DISK SYSTEM RAM expansion cartridge, RAM is provided at %8000-%DFFF and ROM at %E000-EFFF. /ROMSEL is configured for address %E000.
Why not make this an opportunity to make your own Expansion board that connects to an early Microbee32 using its 50 way connector?
These days its really easy to do.
Someone hopes you enjoy this post.
As a guide, attached below are the modifications to a MWB1732 coreboard to work with the prototype Microbee Cartridge Expansion slot.
(As it panned out, RAMs of a suitable size for the cartridges did not become available in time nor at a satisfactory price. Also, that the original intention was to increase the CPU speed to 4MHz but this was not done due to the expense of faster ROMS.)
[#NOTE: There ware performance issues with the MASK FONT ROMS produced by Texas Instruments even working at 3.375MHz. It is preferable to burn your own with faster EPROMS].
1. /PHANTOM SIGNAL ADJUSTMENT
This makes the /PHANTOM signal effective only for coreboard ROMS at memory address %8000-EFFF.
Reconfigure the /PHANTOM signal by disconnecting it from IC20, pin 6 and connecting it to IC22, pin 6.
2. /ROMSEL SIGNAL ADJUSTMENT
This makes the /ROMSEL signal switch between coreboard MWB ROM A to the a signal on the 50 way expansion connector.
Connect the /ROMSEL to pin 10 on the 50 Way Expansion connector (i.e. reallocated from Z80 /HALT).
Cut PCB track from /ROMSEL to IC22 pin 11 then insert series resistor between IC22 pin 11 and ROMSEL.
3.*Only for 2MHz: CRYSTAL ADJUSTMENT
This provides the CRTC with a dot clock capable of displaying 80*25 characters.
Change the onboard 12MHZ crystal with a 13.5MHz crystal.
On the Motherboard, disconnect the CPU Clock from the 74LS92 divide by 6 output and connect to the divide by 4 dot clock output on the 74LS161.
4.*Only for 2MHz Systems: MWB ROM UPDATE
Replace MWB ROMS with 3.375MHz compatible version.
This version of BASIC is reconfigured to handle the increased CRTC Dot Clock and increased CPU clock speed.
The speaker pitches and durations have been adjusted sound correct.
5.*Only for 2MHz Systems: DUAL FONT ROM UPGRADE
This enables the microbee to display a font suitable for 80x24 character resolution.
Description
The Cartridge Expansion port enables a microbee 32K to work with plug in ROM and RAM expansion cartridges enabling it to work with disk drives and CP/M and work with extended play Game Play cartridges. Rather than waiting an eternity for a tape to load, ROM Cartridge based games are loaded instantly.
Theory of operation
When the cartridge port is disconnected, the microbee behaves as normal.
When the cartridge port is connected with no cartridge inserted, the microbee behaves as normal.
When the cartridge port is connected and a cartridge is inserted to the cartridge slot , the ROMs on the coreboard are disabled being replaced with the memory decoded by the inserted cartridge.
This memory can either RAM, ROM or a combination of both.
The /ROMSEL signal is connected to the memory address decoding output of the desired boot address.
For the DISK SYSTEM RAM expansion cartridge, RAM is provided at %8000-%DFFF and ROM at %E000-EFFF. /ROMSEL is configured for address %E000.