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Electronic Control Technology 
- R2IO Board

This was a well designed early S-100 IO board.

RAM & IO Board

The R2 I/O board was an S-100 Bus I/O Board with 3 Serial I/O Ports (UARTs), 1 Parallel I/O Port, 4 Status Ports, 2K of ROM with a Monitor Program and 2K of Static RAM. It was comparable somewhat to the TDL SMB except it did not have a cassette interface.  The R2l/0 provided a convenient means of interfacing several I/O devices, such as - CRT terminals, line printers, modems or other devices, to an S-100 Bus Microcomputer or dedicated controller. It also provided for convenient microcomputer system control from a terminal keyboard with its 8080 "Apple ROM monitor" containing 26 Executive Commands and I/O routines. It could be used in dedicated control applications to produce a system with as few as two boards, since the R2l/0 contained ROM, RAM and I/O. The standard configuration had the monitor ROM located at F000H with the RAM at F800H and the I/O occupied the first block of 8 ports. Jumper areas provide flexibility to change these locations, within reason, as well as allow the use of ROMs other than the 2708 (e.g. 2716 or similar 24 pin devices). Baud rates are individually selectable from 75 to 9600. Voltage levels of the Serial I/O Ports were RS-232.

A simple diagram of the board is shown below:

R2IO Diagram

The ROM monitor, called "Apple" had the following commands.

A-Assign I/O
B -Branch to user routine A-Z
D-Display memory on console in Hex
E -End of file tag for Hex dumps
F -Fill memory with a constant
G -GOTO an address with breakpoints
H -Hex math sum & difference
I -User defined
J -Non-destructive memory test
K -User defined
L -Load a binary format file
M-Move memory block to another address
N -Nulls leader trailer
O-User defined
P-Put ASCII into memory
Q-Query I/O ports: QI-read I/O,  QO send I/0
R-Read a Hex file with checksum
S -Substitute/examine memory in Hex
T -Types the contents of memory in ASCII equivalent
U -Unload memory in Binary format
V-Verify memory block against another memory block
W-Write a check summed Hex file X -Examine/modify CPU registers
Y-'Yes there' search for 'N' Bytes in memory
Z -Z END' address of last R/W memory location

Clearly there was overlap between this monitor and the TDL Zapple monitor.

The manual for this board can be obtained here. The complete Apple monitor (8080 code)  software listing can be seen here


Other ECT  S-100 Boards
8K RAM   16K RAM  R2IO   8080   64K RAM


This page was last modified on 10/25/2013