No more switching memory boards or jumpers!

Currently you have to make a choice about what software you want to run when you plug in a memory card into an RC2014. That's because the capabilities of the memory card are designed to work with different software systems. For instance there are:

• standard linear modules like the 64K RAM board
• paged (sometimes called banked) memory boards like the 512K ROM 512K RAM board which allows access to more memory than the standard 64K address range of a standard Z80 and enables software like Wayne Warthen's RomWBW
• ROM boards which only support ROM type memory and RAM boards which only support RAM

I wasn't happy with multiple RC2014 rigs or switching memory boards and jumpers every time I wanted to run a different kind of software. So I've designed this board which combines the best features of all these kinds of board in one:

• One large 512K memory chip which can be RAM or ROM (selected with 3 jumpers)
• One large 512K RAM chip
• Use a single jumper to select between linear and paged memory OR better still...
• Select between linear and paged memory in software (from Z80 or BusRaider)
• Support for the PAGE pin on the RC2014 bus (with an optional pull-up selected via a jumper)

Works with Wayne Warthen's RomWBW

This kit is compatible with 512K ROM 512K RAM. With the jumper set to Paged position and chip U1 set to ROM a standard RomWBW image functions as it would in a 512K ROM 512K RAM board. In this configuration the PAGE line is supported so single-step debugging with BusRaider is possible. If a RAM chip is installed as U1 then BusRaider can program the chip with a ROM image as it understands the paging mechanism.

Works with Z180 Linear Addressing

With the board in linear mode a Z180 can access the full memory space with its 20 bit address bus and, in addition, a BusRaider can switch the board temporarily to paged mode so that it can access the full memory space using its 16 bit bus. This allows BusRaider to load software like ROM images directly into linear memory space for development, testing and quick switches from one mode to another.

Works even better with BusRaider

So a system with a BusRaider (see separate Tindie listing) and this board in a PRO bus with a Z80 or Z180 processor card, you can seamlessly support machines as diverse as a a TRS80, a Z180 with linear addressing and a paged system running CP/M or similar. All without changing any jumpers!

Page signal allows single-step debugging (with BusRaider)

As mentioned above, none of the currently available cards support the PAGE signal on the RC2014 bus which the BusRaider uses to request that all memory cards are disabled to allow a bus-master to put data directly onto the processors data bus. This feature is used by BusRaider to support single-step for instance.

Jumper Details

• The board has three jumpers to select between RAM and ROM in socket U1. These three jumpers should all be set to the RAM or ROM position.
• One jumper to select between linear and paged addressing. In linear addressing mode the switch to paged mode and back is controllable through software (Z80 code) or with a BusRaider.
• One jumper to enable the PAGE pull-up resistor. The pull-up is enabled when the jumper is in place and disabled when the jumper is removed. A single pull-up on the PAGE line should be present in your system to use PAGE effectively.

Further details of the jumpers and board IO addresses

Notes

• Thanks to karlab on the RC2014 forum I have a supplier of reasonably priced 74HCT670 chips so the board is now supplied with these
• RomWBW is a trademark of Wayne Warthen
• RC2014 is a trademark of RFC2795
• Import duties or taxes may be levied by your country if importing this product and you are responsible for such payment
• This is a kit and requires assembly using a soldering iron, solder and suitable tools

What's included

The kit includes:

• 1 x Printed Circuit Board (PCB)
• 9 x 74HC or 74HCT ICs (logic chips)
• 1 x 10K resistor
• 2 x 100nF capacitor
• 0, 1 or 2 x AS6C4008-55SIN memory chips (depends on your choice at checkout)
• 1 x resistor array (4609X-101-103LF by Bourns)
• 1 x 20 pin header strip for headers (needs to be broken into appropriate lengths - which is straightforward to do)
• 5 x jumpers

Please note that this is a hobby project and no warranties or guarantees of any kind are provided and no liabilities will be accepted under any circumstances.