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Interface rtty3/29/2024 It's been some 40+ years since I wrote the program, don't have the computer, software, etc. The data bit value would then be used to drill down into an "ASCII" table to pull the character then apply the character to the display. Once the 5 bits were in, a routing that shifted the data bits right 3 times in the "A" register then XOR'd the "A" register to change the bits correctly. I remember the routine took in 1 bit at a time with a counter of 5. There were other routines to time the port data in and out. Does anyone know who made that interface and if so what the port number used to address the interface.? I seem to remember all that was needed to read data into or out of the port was to use an "IN A,". The audio transformers I used are 20k primary, and a 2k centre. I wrote an RTTY Z80 Assembly Language program that used that interface. It also contains two optocouplers, one to switch the radio to TX and one for RTTY FSK keying. I also can't remember the port number to address the 1-bit interface. I had one but I can't remember who made the interface. I remember int he late 70s early 80s, a 1-bit interface was sold that plugged into the 40 pin expansion connector on the left rear of the keyboard. I'm also a licensed Extra Class Amateur Radio operator. This circuit may also be used for RTTY and PSK31 applications. I'm new to the group but I'm an old user of the TRS-80 Model 1. JVCOM Interface The above circuit is recommended for use in SSTV applications with use of the sound card with a computer.
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