Sunday, March 12, 2017

The RC2014

Spencer Owen's RC2014 is another Z80-based microcomputer in kit form.

There are two versions of the RC2014: a single board version called RC2014, and the original RC2014 which is based on a motherboard with several plug-in cards.

User interface is via a serial console and supports color text via ANSI terminal emulation. I am using an FTDI USB-Serial cable and a serial terminal emulator software, aptly named Serial, on the Mac OS X.

I bought one of each version of the RC2014 and decided to build the single board one first since it required less soldering and was more compact.

As you can see from the newer picture below, I have been doing "stuff" with it.

The RC2014 comes with a version of Microsoft BASIC in ROM. If you want to do anything with assembly language, you are mostly out of luck: it is rather onerous to upload cross-assembled Z80 code from a PC or Mac.

Enter the monitor program from Lee Hart's Z80 Membership Card. It is written by Josh Bensadon with contributions from various other folks. The monitor is provides a serial console interface and is able to drive the Membership Card hex display/keypad front panel.

I took the source code, removed all the hex display/keypad code, adapted console code to work with the RC2014's 68B50 ACIA/UART, added breakpoint support and voila, we now have a Monitor/Debugger for the RC2014!

The modified source code is hosted on Github.

The really nice thing about Josh's original monitor is that it allows you to upload Intel HEX formatted binary files. So developing on the RC2014 becomes a question of write->assemble->upload->run. And all this without the need for an EPROM programmer or other hacks/workarounds.

I had to make a number of tweaks to get the Intel HEX uploader to work well on the RC2014 and it is robust enough now to upload the whole monitor program itself into RAM for additional development. This is actually how the breakpoint code was developed.

The little plug-in card you see on the right of the RC2014 Mini motherboard is a 16KB RAM card. The original RAM on the RC2014 sits from 8000H to FFFFH. BASIC uses memory in this space. The 16KB RAM sits at 4000H-7FFFH and can be used for further development of BASIC, without colliding with the latter's dependencies.

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