hunt@boulder.Colorado.EDU (Lee Cameron Hunt) (08/18/90)
When I was trying to get more slack from my floppy-drive cable in my A2000, I accidently pulled out the jumper block on J300. I didn't know what position it should be in (either bridging pins 1 and 2, or 2 and 3) so I consulted my trusty A2000 manual. First I looked at the schematics and found J300. It listed the pins (you must look carefully) 1 to 3 from right to left. It also mentioned that one configuration was the "normal" setting while the other was the "A500" setting. Not having an A500, I opted to set it to the "normal" setting. But before I reassembled everything (I had to remove the power supply) I faintly remembered a page on the specific functions of the jumpers. I found the page and read the description for J300. The diagram with J300 suggested that the "normal" setting was between pins 1 and 2, while the schematics said that it was between pins 2 and 3. I was, consequently, confused. I tried both postions on my power-on Amiga and I could find no difference. The explanation about J300 was cryptic, but I think that I'd like the CIA to run off the 60Hz line clock rather than the monitor's sync clock. But what does a lowly newly-graduated EE like me know? So, I ask for help. Email would be nice, but I'll also check this newsgroup. p.s: (to Dave Haynie and the hardware bunch) Jumpers, overall, are a pain. I realize that they are, in general, cheaper to use that software registers; but I sure like the functionality of software-selected hardware features such as the NTSC to PAL selectability on the "fat Agnus" and the ability to switch from 68000 to 68020/30 on the accelerator boards. IBM had a good idea (parish the thought) by requiring no jumpers on their microchannel cards. Is Amiga considering doing similar things? How many jumpers are in the A3000? (I hope few). Thanks much, --Lee "Nothing is more disorginized than Calvinball!" -- Calvin & Hobbes hunt@spot.colorado.edu ...!ncar!boulder!spot!hunt
rsbx@cbmvax.commodore.com (Raymond S. Brand) (08/18/90)
In article <24885@boulder.Colorado.EDU>, hunt@boulder.Colorado.EDU (Lee Cameron Hunt) writes: > ... > > First I looked at the schematics and found J300. It listed the pins (you > must look carefully) 1 to 3 from right to left. It also mentioned that > one configuration was the "normal" setting while the other was the "A500" > setting. > ... > > I tried both postions on my power-on Amiga and I could find no difference. > > The explanation about J300 was cryptic, but I think that I'd like the CIA > to run off the 60Hz line clock rather than the monitor's sync clock. But > what does a lowly newly-graduated EE like me know? > The jumper determines where the clock to the TOD counter on ciaA comes from. There are 3 choices, 1) from the powersupply power-line tick, so that TOD counter is as accurate as the power-line frequency; 2) from the monitor vert- itcal blank signal, not recomended since it's frequency can be affected by software (this is the "500 mode" since the 500 doesn't have a power-line tick); 3) from nowwhere, not recomended. > > --Lee rsbx ------------------------------------------------------------------------ Raymond S. Brand rsbx@cbmvax.commodore.com Commodore-Amiga Engineering ...!uunet!cbmvax!rsbx 1200 Wilson Drive (215)-431-9100 West Chester PA 19380 "Looking" ------------------------------------------------------------------------