PC Ephemera

On 10/26/2005 at 9:18 PM Jim Leonard wrote: the The easiest way to see how it all worked is to go to the PC BIOS listing (it's also the easiest way to use it). Basically, the calls boil down to this: INT 15H, AH=0, Turn casette motor on AH=1, Turn motor off AH=2, Read 1 or more 256 byte blocks into (ES:BX) CX has BYTE count and so must be a multiple of 256 on exit, (DX) has count actually written AH=3, Write 1 or more 256 byte blocks from (ES:BX) CX = byte count (must be a multiple of 256) for AH=2 or 3, on exit, CY=0 if no error. Otherwise, CY=1 and AH=1 if CRC error AH=2 if lost data AH=3 if no data detected There's a 2x2 Berg header on the mobo to set signal levels. Set to M, the threshold is 75 mv (microphone); set to A, the threshold is 0.68 volts (nominally a "line" level). The 5 pin DIN connector works as follows: Pin 1 = motor control relay return Pin 2 = GND, Pin 3 = motor control relay, pin 4 = data in, pin 5 = data out. The BIOS writes a record formatted thus (i.e motor on to motor off): 256 bytes of ones (leader) 2 bytes of SYN (0x16) 256 bytes of data 2 bytes of CRC 256 bytes of data 2 bytes of CRC .... Hope this helps, Chuck