Duart

DUART Dual Serial Board Designed For RC2014

This is an XR88C681-based serial interface card designed for the RC2014 microcomputer system. This provides two serial interfaces to an RC2014 system in addition to a 16-bit counter/timer and several general-purpose input and output lines.

The board has undergone limited testing with the SCM driver written by Colin MacArthur for Tadeusz Pycio's XR88C681 board (and it should be fully software compatible with it).

A driver has been incorporated into the dev branch of RomWBW. This is not currently built into the standard RC2014 ROM but is available in the RCZ80_duart configuration.

Build Notes

Until this is properly documented, refer to the schematic.

The values and types of most components are not critical. Capacitors C1-C6 (100nF, MLCC) are power bypass/decoupling capacitors for each IC and C7 (10µF, electrolytic) provides additional transient decoupling for the DUART itself. RN1 and RN4 (100kΩ) are bussed resistor networks intended to act as pull-ups for the chip select logic (RN1) and to prevent the general purpose inputs (and IM2-specific interrupt lines) from floating (RN4). RN2 and RN3 (1kΩ) are isolated resistor networks intended to provide short-circuit protection to the serial I/O lines. R1 and R2 (100kΩ) pull the serial receive input lines up to their idle state. R3 and R4 (100kΩ) pull the serial /CTS input lines down to their active state.

Oscillator X1 and capacitor C5 are optional in a standard RC2014 system with a 7.3728MHz clock. In this case JP5 should be closed and pins 3 and 4 (CLKDIV2) of JP1 should be bridged with jumpers to provided the DUART with its expected 3.6864MHz clock.

License

Copyright 2019-2020 Chris Odorjan

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.