AIPS@BRANDEIS.BITNET (Greg Lindahl [chimps@brandeis.bitnet]) (11/10/87)
here's my stupid question for this semester: if the MIDI port is run by some sort of ACIA and is actually some fancy sort of rs232 port, could it possibly be reprogrammed a bit to be a "normal" rs232? i'm an os9 user, and i would *love* to be able to have 2 terminals. i've heard of some MTC people who have done this, and it was 2 jumpers and a couple of interrupt handlers. however, i can't seem to actually find these people. also, it allegedly was still hardwired to 31.5kbaud... i guess we have to burn another keyboard prom to change this to something useful with a modem? any advice/information would be appreciated. greg Greg Lindahl | bitnet: chimps@brandeis.bitnet brandeis radio astronomy group (BRAG) | ci$: [76515,1122] --------------------------------------| us snail: box 2522 brandeis university "OK, if stupidity isn't an impeachable| waltham mass (usa) 02254-9110 offense, then what is?" | telco: (617) 899-5884
jwt@atari.UUCP (Jim Tittsler) (11/11/87)
In article <8711100411.AA12628@ucbvax.Berkeley.EDU>, AIPS@BRANDEIS.BITNET (Greg Lindahl [chimps@brandeis.bitnet]) writes: > > if the MIDI port is run by some sort of ACIA and is actually some fancy > sort of rs232 port, could it possibly be reprogrammed a bit to be a > "normal" rs232? > The MIDI port and the ikbd line are each provided by (Motorola) 6850 ACIAs. They are being clocked with a 500 kHz signal. The MIDI port uses the divide-by-16 mode of the 6850 to produce 31.25 kbaud, and the ikbd port uses divide-by-64 to produce 7812.5 baud. The things that make your suggestion a tad messy: 1. The baud rate divisors provided by the 6850 have no finer granularity than /16 and /64. This precludes getting "standard" baud rates. (Unofficial hint: If you were willing to hack up your hardware, you could separate the MIDI 6850's TxClock and RxClock lines from the 500 kHz signal and provide them with your own baud rate clock. If you were willing to live with the restriction that the "MIDI" port would always have the same baud rate as the MFP serial port, you could probably get away with stealing the clock from the MFP's timer D output which is used as the MFP baud rate generator.) 2. There are no modem control lines available on the MIDI output connectors. 3. You will have to convert the MIDI current loop to RS-232C (or whatever your terminal expects). Jim Tittsler {ames, imagen, pyramid}!atari!jwt