Brian Beard's Retro Dumb Terminal Is an Eight-Bit Debugging Tool for Eight-Bit Projects
RTD64 offers a surprising number of features, including color settings, carriage return translation, multiple fonts, and more.
Engineer Brian Beard has taken to the pages of Circuit Cellar to detail the design of a custom debugging tool which owes its inspiration to a bygone era: the eight-bit Retro Dumb Terminal, or RTD64.
"I always have at least one 8-bit development project on my workbench. The first thing I get working on any new prototype is the serial port. Once that’s working, I use my suite of embedded assembly language routines to monitor and debug via the serial port," Beard explains. "I don’t have a spare laptop I can dedicate to every development project, so I wanted another solution. All I need to do is enter selections to exercise different software routines and observe the results — I don’t need data storage or to transfer files. A PC is serious overkill for this. All I need is a dumb terminal, so I decided to build one."
Given that his projects center around eight-bit microcontrollers, the resulting Retro Dumb Terminal is an eight-bit device too: The custom board carries two Microchip PIC microcontrollers, a PIC16F1823 and a PIC16F1788, ATF16V8 generic logic array (GAL) chips, SRAM, an EEPROM to hold the firmware and settings, and a PS/2 keyboard port — courtesy of a Maxim MAX232 interface chip — and VGA for video, plus a serial connection and barrel-jack for power.
The resulting terminal board offers a 512-by-400 resolution active area, giving it a 64-by-25 character display. The ASCII character set is stored on the EPROM, alongside the pixel map; the code for the character at any one of the 1,600 possible screen locations is stored in SRAM. A built-in configuration system allows for choosing between different board rates, enabling local echo and bell sounds, translating carriage returns in either direction, switching fonts, and even choosing from custom foreground and background colors.
After creating an initial prototype in wire wrap, Beard designed a PCB which fits into an off-the-shelf case. "The RDT64 is working fine as a simple serial ASCII input and output system for debugging," Beard notes. "I plan to make it the terminal for a general purpose Z80 system in the near future."
The full project write-up is now available on Circuit Cellar, while the RTD64 is available to buy from Lucid Technologies as a kit at $59 or $75 fully assembled and tested.
