KDS Electronics Serial Interface

KDS Serial Interface

All of them were wired incorrectly. d7 was d0, d6 was d1, and so on. Consequently you had to reverse the bit order before you could do anything useful with it.

In addition, the hardware handshaking didn't work properly, and since the ports were different to those used by the Amstrad/Pace interface, you were limited to the built-in KDS software. Which sucked.

Technical

Connects to expansion port. Contains software in ROM bank 6. Has one single 25pin DSUB connector (with TX,RX,RTS,CTS). The baudrates are generated by the 8253, and can be further divided by the 6850 (DIV1,16,64). (for example 6850=DIV1, and 8253 Counter=01A1h gives 4800 baud; 2MHz/01A1h/1).

 FBE8h KDS RS232 8253 Baudrate Generator Counter 0 (RX Clock)
 FBE9h KDS RS232 8253 Baudrate Generator Counter 1 (TX Clock)
 FBEAh KDS RS232 8253 Baudrate Generator Counter 2 (not used)
 FBEBh KDS RS232 8253 Baudrate Generator Counter 0-2 Control Registers
 FBECh KDS RS232 6850 (reversed-bit-order) Control (W)
 FBEDh KDS RS232 6850 (reversed-bit-order) TX Data (W)
 FBEEh KDS RS232 6850 (reversed-bit-order) Status  (R)
 FBEFh KDS RS232 6850 (reversed-bit-order) RX Data (R)

Caution: KDS has wired the 6850 chip's data bus incorrectly: D7 is D0, D6 is D1, etc. (so the bit order must be reversed by software). And, reportedly, the hardware handshaking doesn't work properly (no idea if that's a hardware or software glitch, or maybe the 6850's 1-stage RXFIFO is just too small for high baudrates?).