Not what would be called modern these days but I managed to run across two MicroVAX 3100 machines with DST32/DHT32 synchronous serial interfaces in them plus two V.24 and one each of V.35 and X.21 cables that will plug into them. With some help from the people here, I managed to get the machines talking to each other using a null modem between the two V.24 cables. I also have two nearly identical syncronous modems, one with a V.35 interface and another with an X.21 interface but I have not managed to get these to talk to each other, probably because they can't be configured to match any of the speeds the DST32/DHT32 interfaces can do.

Mattis, thanks! That's an implementation along the lines I was thinking. If yours can get close to 1 Mb/s, chances are one could get all the way there with the Arduino Itsy Bitsy M4, that's a 120 MHz ARM chip (Cortex M4). It has USB built-in. I'll study your code; that approach of using a fast loop for consistent reliable timing matches what I was thinking. Actually the STM32F103 has built-in USB so there is no difference there,

DDCMP is a bit harder because it's normally full duplex.

The framing is different but no harder, I think. And I was thinking of leaving the protocol state machine to the host, so the microcontroller would only do framing -- deliver completed good frames to the host without interpretation.

paul

leaving the protocol state machine to the host, so the microcontroller would only do framing -- deliver completed good frames to the host without interpretation. byte counter rather than various characters to end the frame. That would probably simplify the software. It seems to use SYN SYN which is identical to BSC so that part of the code that takes care of framing could probably be used directly. Yes, though the sync byte has a different value, the fact that it's called SYN is a bit misleading if you're used to the SYN used in BISYNC.

There are also the small STM32F411 Weact boards out there ( https://github.com/WeActTC/MiniF4-STM32F4x1). 100 MHz and the ART accelerator. From other projects where I have used the STM32F103 have seen that it executes slower than I expected since it was reading code from flash. The ART accelerator should help here to achieve near zero wait state so perhaps 1 Mbit/s would be possible? What is an ART?

I looked a bit at that Weact thing but got lost in the fulminating about "pirated" copies. Seriously? Open source designs are meant to be copied; "pirated" is a nonsensical term. Low quality copies, that would be a valid complaint. (The use of leaded solder, all things equal, increases quality rather than reducing it, by the way.)

The ARM chips used in the Adafruit boards I've used have on-chip flash so I'd assume that runs quickly, but I'll have to try to find out.

DDCMP support as well! Then perhaps I could try those M8203 / M8207 boards I have sitting here. Thanks, will keep that in mind. What sort of connection and signaling do your DMR boards use?

paul

1 Mb/s is the top speed of the DMC with the coax local "integral modem" connection. I don't know if the real modem card could go that fast. Probably not; the top speed requires special microcode. But the DMR, with a faster engine, can do 1 Mb/s without trouble. I suspect that if you take the modem flavor of the DMR and manage to clock those signals at 1 MHz you can indeed send that fast. Of course, RS232 officially isn't rated anywhere near that high (9600 I think is the official limit). Other physical links like V.35 or RS422 were used at the time to go faster. In every case, you can usually get away with going well over the limit if the cables are short enough, and especially if the cables are better quality than the minimum. For example, the DMC/DMR local connection is specified to use triax, but it wouldn't surprise me at all if Cat 5 Ethernet twisted pair cable works just as well. The main question for new work is what people have out there to connect to. The only thing I have is a Pro. That has a comm port with a USART, which will do sync just fine but tops out at 9600 bps or so due to having a tiny FIFO. That's RS232. I have no DMC or DMR or anything else fast in my collection. Thanks for the pointer to the Z85C30. Nice chip but it costs more than an Arduino (!); I was thinking of a software-only solution if possible. Mattis, thanks! That's an implementation along the lines I was thinking. If yours can get close to 1 Mb/s, chances are one could get all the way there with the Arduino Itsy Bitsy M4, that's a 120 MHz ARM chip (Cortex M4). It has USB built-in. I'll study your code; that approach of using a fast loop for consistent reliable timing matches what I was thinking. DDCMP is a bit harder because it's normally full duplex. The framing is different but no harder, I think. And I was thinking of leaving the protocol state machine to the host, so the microcontroller would only do framing -- deliver completed good frames to the host without interpretation. paul