hugh@hcrvx1.UUCP (Hugh Redelmeier) (09/19/85)
I just bought a 600xl with 64K of RAM. I did NOT buy a disk drive or
cassette drive: if I were to spend serious money, I would want to get
a serious machine. But I can't resist hacking on the new toy. I am
thinking that I might try to make one of my other computers simulate
a disk.
I understand that the disk port is really a 19.2K Baud serial line
at TTL levels (not RS232C levels).
- Is this true?
- What protocol is used to talk to the disk?
- Is it asynch or synchronous?
- What is the structure and meaning of the info transferred?
- What are the pinouts? (By the way, what are the pinouts of
the other connectors?)
- How much disk support is in the ROM? On a DOS disk?
- What is the cassette interface: would it be easier to simulate?
- How does my 600xl differ from an 800xl?
- (Most important): what are good sources for this information
(books, specific magazine articles, ...)?
The September BYTE article on upgrading to 256K RAM and the RAM-disk
software (posted by ihnet!bryan) contain some hints.
Hugh Redelmeier (416) 922-1937
{utzoo, ihnp4, decvax}!hcr!hughekijak@ARDC.ARPA (Edmund S. Kijak, POINT) (09/24/85)
Regarding the casette interface, I don't see how it can be done entirely in software. The casette output is an analog voltage whose magnitude depends on the volume control setting - you would need some hardware simply to convert it to a standard voltage level, say TTL. The interface converts FSK (frequency shift keyed) audio tones to digital bits. The bits are asynchronous serial with a start bit, data bits, and a stop bit. Baud rate is 600, a ZERO is a 3995 Hz tone, a ONE is a 5327 Hz tone, the tone durations are equal. The output of the casette needs to be converted to TTL levels (0 or 5 volts for logic ONE or logic ZERO) before feeding to computer. (I may have the ONEs and ZEROes swapped, and may be off a few Hz, but the info is basically correct).
djk611@uiucuxa.CSO.UIUC.EDU (10/01/85)
the disk port is indeed running at 19.2 kb and at ttl levels there is no rom support for the disk persay the cio (central i/o) is in rom and is easily accessed the same connector is use for cassatte but outputs are frequency(read tones) as opposed to signnals...the best source of info is atari tech notes or de re atari scott cothrell urh 106 forbes hall 101 e. gregory dr. champaign il. 61820 university of illinois