![S100 Computers](../../../Header/S100_Banner.jpg)
TDL System
Monitor Board (SMB).
This was an amazing
card at at a time when a typical computer output went to a Teletype.
![TDL SMB](SMB.jpg)
The board had the following
features:-
A 2K MONITOR operating system
(the ZAPPLE Monitor) in ROM.---2K of RAM, read/write storage for
user programs, auxiliary monitor routines, and/or stack area.
Two SERAL I/O PORTS, 110-9600 baud,
RS232 or 20ma current loop for each port, and software-initialized via the monitor.
Can be used for TTY, CRT terminal, or other serial device.
One PARALLEL I/O PORT,
bi-directional, can be configured as an input or output
port port or dynamically changed under program control.
A Sense Switch Import Port that allows the user to specify
the I/O configuration which the system will initialize to.
A 1200 BAUD, CASSETTE INTERFACE. Allows rapid loading
and dumping of programs/data in either a checksummed hex file or a binary image
format.
JUMP TO MONITOR. Contains
circuitry for automatically jumping to the monitor at F000H prompted
by a power on clear (POC) and/or reset.
The board was often used in those early days with Teletype Corporation's
ASR33 "Teletype". Later versions of the ASR33 had an RS-232 hookup option but
earlier machines relied on a 20mA current loop connection. See
here
for some
issues using the latter.
One problem TDL ran into with this board was that the four EMM-SEMI 4804
RAM chips shown above were at the time very hard to obtain because they
were in short supply. TDL supplied early users with a small adaptor board
that contained Intel 2114 RAM chips. Such an adaptor board is shown below.
![TDL SMB with RAM Adaptor](SMB+RAM.jpg)
The manual for this board can be obtained
here.
The schematic
can be seen
here.
The manual for the original Zapple
monitor can be obtained
here.
A later version
here.
I recently noticed that the custom Zapple ROM on this
board can be changed for a standard 2716 EPROM with one small change.
Either bend up pin 20 on the 2716 EPROM and tie it to +5 volts or cut the trace
going to pin 20 on the SMB and jumper the pin to pin 24 of the same chip.
This allows you to modify the Zapple monitor for your specific needs and yet
mentain the functionality of the board. With just this board, a Z80 board and a
video board you have the start of a very capable S-100 system. I use this
setup to test many of my other boards before putting them in my main system.
Here is a picture of the test system.
![TDL+2716](SMB+2716.jpg)
Later Version of the SMB.
Apparently there also was a more updated version of the
board called the SMB-II. It was advertised in the May issue of Byte. But
few were actully produced.
Other TDL S-100 Boards
SMB
Z16-RAM
ZPU
32KRAM
VDB-2
This page was last modified
on 01/08/2011