gt4785b@pyr.gatech.EDU (CARTER) (11/28/87)
Is there a magazine article or technical reference manual that gives a good, clear explanation of the differences between slow ram, fast ram, and slow-fast (half-fast?) ram? And since I didn't get any reply to my question "What bit rates are available on the serial port?" can somebody at least tell me what the MIDI bit rate is? I've heard 'guesses' of 32,768 and 30,500, but my communications text says that 20,000 bps is a practical upper limit for RS-232. David Carter (waiting for ml as fi i
dillon@CORY.BERKELEY.EDU (Matt Dillon) (11/30/87)
The serial controller can generate any baud rate: rate = (N+1) * 279.4 ns (N: 0..32767) E.g. 109.2 to 3,579,098 baud. However, the processor can only shove data out so fast. a lowly 68000 cannot read data at the maximum baud rate without overrun either. I recall a previous message asking about baud rates, but the path was not on the arpa net (as this one is), and USENET mail bounced. -Matt
wolf@ssyx.ucsc.edu (Mike Wolf,4264777) (12/02/87)
In article <4558@pyr.gatech.EDU> gt4785b@pyr.UUCP (David Carter) writes: > >And since I didn't get any reply to my question "What bit rates are available >on the serial port?" can somebody at least tell me what the MIDI bit rate is? >I've heard 'guesses' of 32,768 and 30,500, but my communications text says >that 20,000 bps is a practical upper limit for RS-232. > >David Carter (waiting for my A500!) Hmm, last time I checked, my GraphOn 250 can zip along as high as 56.7 KBaud. Even old VT100's can do 19.2 KBaud. +------------------------------------+---------------------------------------+ | Michael Wolf | An old Scandinavian quote: | | BITNET: wolf@ucscj.BITNET | "You can lead a herring to water, | | ARPA: wolf@ssyx.ucsc.edu | but you have to walk real fast, | | UUCP: ...ucbvax!ucscc!ssyx!wolf | or else he'll die." | +------------------------------------+---------------------------------------+
hedley@cbmvax.UUCP (12/03/87)
In article <1303@saturn.ucsc.edu> wolf@ssyx.ucsc.edu (Mike Wolf) writes: >> >>And since I didn't get any reply to my question "What bit rates are available >>on the serial port?" can somebody at least tell me what the MIDI bit rate is? >>I've heard 'guesses' of 32,768 and 30,500, but my communications text says >>that 20,000 bps is a practical upper limit for RS-232. >> Sorry about the delay, I guess everyone else thought somebody else would answer this question. ( At least we all hoped ). ANYWAY, Standard baud rates for amiga include: 110,150,300,600,1200,2400,4800,9600,19200 & 31250. Midi baud rate is: 31250. <- included as standard. In reality, the amiga is capable of many more baud rates as the bit timing can be controled with a rather fine granularity. The list above merely reflects the baudrates which preferences directly supports. Hedley
daveh@cbmvax.UUCP (12/04/87)
in article <1303@saturn.ucsc.edu>, wolf@ssyx.ucsc.edu (Mike Wolf,4264777) says: > Keywords: slow ram, fast ram, MIDI > In article <4558@pyr.gatech.EDU> gt4785b@pyr.UUCP (David Carter) writes: >>And since I didn't get any reply to my question "What bit rates are available >>on the serial port?" can somebody at least tell me what the MIDI bit rate is? >>I've heard 'guesses' of 32,768 and 30,500, but my communications text says >>that 20,000 bps is a practical upper limit for RS-232. >> >>David Carter (waiting for my A500!) > > Hmm, last time I checked, my GraphOn 250 can zip along as high > as 56.7 KBaud. Even old VT100's can do 19.2 KBaud. Yeah. Remember, everyone, that RS-232 is a complete protocol with all kinds of specs. All together, taking the longest permissible cable and other worst case things, the specification probably reads that 20,000 bps is the upper limit on what you can use without dropping bits. Sounds reasonable, but how many of you are using 100ft cables? For the 2 foot cable that goes between your Amigas, 31.8K or whatever is probably no problem. The RS-232 spec doesn't place any inherent limit on how fast your RS-232 hardware can run, only how fast physics might be likely to let it run over a long cable. And even at that, it might still work. It's just that if it doesn't meet the spec, it's not really RS-232. > Michael Wolf -- Dave Haynie Commodore-Amiga Usenet: {ihnp4|uunet|rutgers}!cbmvax!daveh "The B2000 Guy" PLINK : D-DAVE H BIX : hazy "I can't relax, 'cause I'm a Boinger!"
karl@sugar.UUCP (Karl Lehenbauer) (12/05/87)
> In article <4558@pyr.gatech.EDU> gt4785b@pyr.UUCP (David Carter) writes: > >And since I didn't get any reply to my question "What bit rates are available > >on the serial port?" can somebody at least tell me what the MIDI bit rate is? > >I've heard 'guesses' of 32,768 and 30,500, but my communications text says > >that 20,000 bps is a practical upper limit for RS-232. MIDI runs at 31250 bits per second. That is one million divided by 32, a useful number for people doing dedicated MIDI interfaces (i.e. ones that only run at the MIDI clock rate) Note that this is still an asynchronous protocol; two framing bits are transmitted per byte of data. MIDI is not RS-232. RS-232 uses +/- 12 volts for ones and zeros. MIDI uses five and zero volts. Also note that MIDI cable lengths over 50 feet are not recommended and MIDI does occasionaly drop a bit. Since it's not an error free protocol (other than certain manafacturer's system exclusive formats and the sample dump standard) that can cause all sorts of problems, the most common of which is hanging notes, but that's another story for another time. -- ..!uunet!nuchat!sugar!karl Unix BBS (713) 933-2440
grr@cbmvax.UUCP (George Robbins) (12/06/87)
In article <4558@pyr.gatech.EDU> gt4785b@pyr.UUCP (David Carter) writes: > Is there a magazine article or technical reference manual that gives a good, > clear explanation of the differences between slow ram, fast ram, and slow-fast > (half-fast?) ram? Chip memory is memory that can be accessed by the Amiga custom chips for various purposes including video refresh. In the higher resolution* video modes this video refresh uses up some or all of the cycles normally usable for processor access resulting in contention, which is to say that the processor effectively runs slower when accessing chip memory. Fast memory is memory that is not on the Amiga chip's memory bus, and thus avoids contention, allowing the processor to run at full speed without regard to the video mode. The internal expansion memory in the A500 and A2000 is on the chip memory bus but is not accessible by the Amiga custom chips due to limitations in the addressing capabilities of the Agnus chip. Since it is on the chip memory bus it suffers from the same contention constraints as the other chip memory. Originally, the C00000-D7FFFF area where this memory is position was documented as being for "fast" internal expansion for future machines, however when we designed the A500, we found that putting the internal expansion memory on the chip memory bus, but having it respond to these addresses would allow us to include provision for up to 1MByte of internal expansion memory without the additional expense** and complications of the circuitry required to implement "fast" memory and would still be compatible with the existing 1.2 software. The confusion of having "chip" or "slow" memory residing in this putativly "fast" memory allocation has led to the rather perverse "slow/fast" or "half/fast"*** memory designations. Notes: * It should be noted that the Amiga hi-res modes are not present in the Atari ST family and that no contention occurs when using the lower resolutions such as those implemented in the ST. This means that the only performance difference results from the Amiga's 7.16 Mhz CPU clock rate vs the ST's 8 Mhz clock. However it is this relation of the Amiga's clock rate to the various NTSC video timings that allows simple implementation of the Amiga's video related features and accessories. ** rule of the computer biz: if it costs us money to put in a feature, then the list price goes up - it had better be worth it to the majority of your customers. *** this is supposed to be funny, I think - time will tell... -- George Robbins - now working for, uucp: {uunet|ihnp4|rutgers}!cbmvax!grr but no way officially representing arpa: cbmvax!grr@uunet.uu.net Commodore, Engineering Department fone: 215-431-9255 (only by moonlite)