1802-Mini-Expander-RTC

This is the memory and port expander plus real-time clock card for the 1802/Mini system. It supports the following features:

Memory Expansion

32K added ROM or RAM
Can be addressed in either upper or lower 32K block
Can be split on any power of 2 size from the top or bottom of the block
Splitting the block allows mixed ROM and RAM in the same 32K block
Expansion memory can be enabled or disabled under software control
Can be set to be enabled or disabled be default at system reset

The software control can be used to implement bank switching, such a 32K ROM that includes diagnostics run at boot time but is then replaced with RAM except for the last 2K or 4K which has BIOS. Or you could have a system that can start either a Riley “Disk-less ROM” with 32K RAM/32K ROM, or a Elf/OS system with 60K RAM/2K ROM under control of a software menu.

Real Time Clock

Keeps month, day, year, hour, minute, second time and date
Corrects for leap years
Can provide a periodic interrupt at 64 Hz or once per second, minute, or hour
Can also provide a pollable signal on an EF line at the same rates
Uses a replaceable BR1225 coin cell battery
1.3uA standby current gives approximately 5 years battery life
Uses one I/O port 1-7 which is two-level group addressable

I have written a loadable driver that presents the “standard” interface to Elf/OS 4 to enable date and time, and there is also a new BIOS that supports all features of this card available here:

https://github.com/dmadole/1802-Mini/tree/master/firmware

Port Expander

Implements low 4 bits of the Microboard group scheme
Written group select value can be read back also
Implements a “group 0” which is automatically selected at reset
Total of 5 groups gives 35 maximum I/O ports (5 groups of 7)
Allows for high 4 bits to be implemented on another card
Uses one I/O port 1-7

Gerber files for the PCBs and PDF schematics can be found in Releases.

BOMS and any applicable errata or other notes can be found in notes.

For availability of kits and bare PCBs please see http://madole.net/1802/mini/kits

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