| ROM-less, RomWBW-capable Zx80 SBC [message #10476] |
Thu, 02 November 2023 07:24  |
plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA
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Senior Member |
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While waiting for pc boards to arrive, I want to introduce a group of ROM-less RomWBW-capable Zx80 SBC. These are smallish (2"x4") Z80, Z180, or Z280 SBC that do not have a flash memory on board; they always have a CPLD and CF disk which replaces the flash memory and also serves as the mass storage. All these boards will run the ROM-less version of RomWBW. A couple of them already existed for few years, but 3 more new designs are arriving soon.
These boards consisted of 4 primary components, Zx80 processor, 512K (or bigger) RAM, CPLD, and CF disk. There may be other peripheral components like RTC, I2C expansion, or neopixel LED. The motivation for earlier designs was to encapsulate a particular operating environment by a corresponding CF disk; a different operating environment can run in the same hardware by swapping in a different CF disk. A related benefit is that CF disk contents are easy to change, so software development/update are significantly easier than flash-based designs.
The current designs are driven by Wayne Warthen's latest enhancement to his already excellent RomWBW. This enhancement supports ROM-less RomWBW (an interesting twist considering RomWBW was originally based on ROM, as its name implies). This version of RomWBW produces a 512K image and requires the external hardware/software to load the image into RAM then jumps to 0x0 to start RomWBW. In my opinion, RomWBW is THE killer application for Z80, Z180, and Z280 and this new enhancement has enabled a class of small, fast, and low-cost Zx80 SBC, thus motivated me to design a series of computers in support of the ROMless RomWBW.
This is the introductory post for these SBC. Like the table of contents, it may be edited later to point to later entries. Because of limitation on number of attachments per post, I'll create a series of posts below dedicated to each specific board with attachments and links.
Bill
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| Re: ROM-less, RomWBW-capable Zx80 SBC [message #10487 is a reply to message #10486] |
Mon, 06 November 2023 08:59  |
tapy
Messages: 17
Registered: June 2021
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Junior Member |
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You have a hand in this, as I modelled my serial bootstrap method on yours, simply modifying the process to run autonomously without PC involvement. In theory the clock is synchronous, but in practice this would need to be checked as the AVR datasheets do not specify the delay introduced by the internal counters I use to divide the master clock. So far I haven't noticed any problems, and I'm using this serial port quite intently as I'm trying to build an MP/M for the Z280. I'm currently trying to learn how to use the MMU in system mode only, so far without success - changing the bank (whether procedural or via an array) causes a crash and I don't understand why. I need to spend more time solving this problem.
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