The Intel A is the industry standard Universal Synchronous/Asynchronous Receiver/Transmitter. (USART), designed for data communications with Intel’s. Data Sheet for Serial Control Unit. REL iWave Systems Technologies Pvt. Ltd. Page 2 of (Confidential). DOCUMENT REVISION HISTORY. A datasheet, A pdf, A data sheet, datasheet, data sheet, pdf, Intel, PROGRAMMABLE COMMUNICATION INTERFACE.

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Results 1 to 10 datsaheet Thread Tools Show Printable Version. First, I initialized the board: Unfortunately nothing displays on the screen of the terminal.

Intel 8251A USART re-introduced by Rochester Electronics

Can datashedt me help in this case? PM me if you have a modem of interest, particularly interested in Acoustics, early externals, and internals for Apple II’s no interest in PC or Mac internals Top of the want list: Also looking for Racal-Vadic documentation! AltairIthaca Intersystems boards, software, manuals.

Ah, the “Neanderthal” Intel just like the “Neanderthal” both with their quirks. Kipp, the reason for the odd initialization is that the uses the same port to set the mode and as a command register.

After a reset either hardware or softwarethe is in a “mode” state.

Unfortunately, the mode initialize sequence catasheet synchronous mode is 3 bytes long, so if some garbage accidentally gets sent as a mode command, everything gets screwed up. So the first pair of bytes serves daatsheet flush the possible synchronous mode initialization and the third byte actually performs the async initialization.

The fourth byte is a command byte. At this point, I should probably ask if you’ve set up the handshaking properly. Otherwise, the won’t transmit. The naming of the command bit is a little misleading Anything what I do, nothing will work. Chuck GI changed the 37 to 27, but no succes.

I think something else with the initialization of the is wrong, unfortunately I did not have further now how in programming machines. Okay, let’s go back to stage 1.


First of all, I assume that you’ve read the SIO-2 manual? How are the myriad datassheet set up on your board?

Have you tried the simple echo program in the back of the manual? I read the manual over and over again. Okay, let’s 82251 if the is actually working. Instead of running an infinite loop, modify your code to send say, characters and then halt. You should be able to easily see a delay between the time that you start the code and when it halts.

If that works, and the code doesn’t simply hang, you need to sniff down the line from the If you’ve got a logic probe, go back to running your original program and see if the TxD line on the is wiggling. It’s quite possible that the EIA driver ? This takes me back to my youth!

If you can get into assembler programming at the mnemonic level — you will find this much easier and less error prone. You can download pretty good cross-assemblers for Windows or Linux or whatever your flavour of operating system is and use your favourite text editor to create the assembler programs, assemble them and even test them and then download the resulting binary or hex file to your IMSAI machine for final running.

If so, just do a search for the datasheet from Intel. If the RESET button is wired to the reset pin of the which it probably is hitting reset will cause any previous initialisation to be thrown away.


I am also confused by your initialisation sequence. I am assuming here that you are starting your programs at address So, what does my 8521 do? Obviously, this value must be setup correctly to match your terminal.


This datasheeet the UART to asynchronous mode rather than synchronous mode and divides the externally-supplied baudrate clock by This is the usual default. If you change this value, then the indicated baudrates may not be as expected. Issuing two commands like this is the correct initialisation procedure as this configures the and resets any errors.

If you are writing a receive routine then you should be looking for any parity, framing or overrun errors if they exist and take action accordingly. So, my hex code for the above code loaded into location would be: I generally interconnect dafasheet hardware handshake lines if they are not in use.

Intel – Wikipedia

Do this at the SIO connector end. Strap just pins 2 to 3 on the terminal and check that when you type on the keyboard that the characters you type actually appear on the display. If so, remove the link and make sure the characters stop when you type some more! The other thing to check is to make sure that transmit of the terminal is wired to receive of the SIO and vice-versa.

This should be the transmit line in each case. Connect one end to pin 7 ground and use the other end as a sensor lead. One or the other of the LEDs should light up when it is connected to the transmit line. After that we are looking into either a major hardware fault or a major configuration fault. Hope this is of some help to you. Bookmarks Bookmarks Digg del. All times are GMT The time now is