Technical Design Labs System Monitor Board TDL SMB S-100 Altair IMSAI EPROM Mod For Sale

Technical Design Labs System Monitor Board TDL SMB S-100 Altair IMSAI EPROM Mod
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Technical Design Labs System Monitor Board TDL SMB S-100 Altair IMSAI EPROM Mod:
$349.99

For sale is a Technical Design Labs System Monitor Board, better known as the TDL SMB. This board provides all of the basic I/O facilities for a S-100 microcomputer like the Altair or IMSAI on a single board, and was a very popular addition! It has the following features:
  • 2 KB ROM containing the Zapple monitor 1.2G
  • 2 KB of static RAM in 4x SEMI4804 devices
  • Two serial channels, Motorola 6850 ACIA based, 110 - 9600 BPS, RS-232 or current loop
  • Cassette storage interface
  • Power-on jump
  • Uncommitted parallel I/O port
  • Sense switch register for configuration
This particular TDL SMB is an earlier run rev 1 board -- the darker green solder mask is an indication of this, later runs use a lighter green glossy solder mask. It arrived in our shop in nonworking condition, without mask ROM or SEMI4804 static RAMs. All tantalum capacitors were replaced, as they are a known failure hazard on TDL boards. One 74LS367 buffer was found to have a broken pin and was replaced with a NOS part from inventory.
The SEMI4804 sockets on this board likely had a TDL 2114 adapter installed at some point, as the sockets were very loose. They were replaced with high-quality machine pin sockets, and NOS purple ceramic SEMI4804s installed. The static RAM was tested at 4 MHz.
Since the original mask ROM was missing, and since we don't have a source for them, this board was modified for operation with 2716-type UV EPROMs. The process for this is documented on our website; however, we cannot provide a direct link due to links policies. The included white ceramic EPROM contains Zapple monitor version 1.2G, which is a later revision from the SMB-II era, but fully functional on the older TDL SMBs. To ensure proper long-term operation, the ROM socket was replaced with a high-quality machine pin socket before modifications were performed.The previous owner had removed the power-on jump circuit, which was rebuilt and tested.Final testing was done in one of our shop IMSAIs, with a Cromemco ZPU board. The TDL SMB was used to boot into CP/M 2.2 with a VersaFloppy II diskette controller. Exhaustive tests were run for several hours. Both the TTY and VIDEO serial channels were tested, as the console and with KERMIT through CP/M. This TDL SMB operates correctly at 4 MHz, including power-on boot.DO NOTE: the Zapple monitor requires a Z80 processor to run and is not compatible with the Intel 8080! If you want to run the TDL SMB with an Intel 8080, we can provide a 2716 type EPROM programmed with a copy of the Apple monitor. The Apple monitor was an earlier TDL product, and has basically the same features and functions as Zapple.
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