[cctalk] Re: programming the IBM PC synchronous serial boards (Northstar Advantage project)

On 12/22/23 16:02, Glen Slick via cctalk wrote: Sync (Bisync, SDLC/HDLC) was fairly popular back in the day for linking with mainframes. (Think, for example, IBM HASP). On PCs and the like, the Intel 8251 was used a lot, but even the Signetics 2651 has the sync mode, with the ability to recognize a double-byte sync. One key difference from async mode is that while async operates with start and stop bits to synchronize character data, sync sends as a block of data with no start/stop overhead. Idle times are automatically filled with SYN characters. The protocol for any of the above higher-level protocols is fairly complex and there are manuals for that. As far as software, I may have some for 8085/8251 kicking around. Interestingly, I've used synchronous mode to read certain proprietary floppy formats. After all, the two are cousins. You have Idle characters, ID fields, etc. Sync mode can be pretty efficient on a leased line. It was pretty much the default back in the Bell 408 days. --Chuck