When you say 'vias' I assume you mean SOLDER-TRACES and not Versatile Interface Adaptors? --- Marko_Mäkelä <msmakela@cc.hut.fi> wrote: > On Fri, 30 Mar 2001, john/lori wrote: > > > Why 3.3 volts? > > Is there some good reason for that (the ROM only > comes in an LV version > > or something)? > > Yes, the Am29LV160 boot-sector flash ROM is only > available as a > low-voltage version. If you know of a programmable > ROM that is available > in an SMD package and has at least 2 megabytes of > capacity, please let me > know. Other chips could be powered from 5 volts. > > > Presummably the 74LVX245 does the level > translation, but 74LVX__ > > aren't dual supply are they? (the 74LVX__ are 5V > tolerant in, but > > isn't there some other family for driving 5V?) > > The ON Semiconductors (former Motorola) 74LVX245 > data sheet, page 1 > <URL:http://www.onsemi.com/pub/Collateral/MC74LVX245-D.PDF> > mentions > something about "a parasitic diode" being formed > between the bus and Vcc > terminals. I don't know if this is a problem; > aren't there some internal > NMOS pullups on the data bus? According to the > schematic diagram > 251027-01 sheet 1, left side, the data bus on the > cartridge port is wired > directly to the 6502 and to a 74LS245 in the VIC-20. > > I managed to reduce the number of vias to 25 (not > bad, since 19 signals > need to be routed from one side to another). The > board is now about 53 mm > tall. Three boards could be fitted on a standard > 160 by 100 mm circuit > board. By making photo masks of exactly that size, > it should be possible > to align the bottom and top sides without special > equipment. And there's > no need to drill any holes, since all chips are SMD. > Just solder wires > around the edge of the card. No vias are located > under any chip. > > Marko > > - > This message was sent through the cbm-hackers > mailing list. > To unsubscribe: echo unsubscribe | mail cbm-hackers-request@dot.tml.hut.fi. ===== Get a FREE 6Mb webmail box from go6502! - http://www.geocities.com/profdredd As low as 2.99% Intro APR from NextCard! - http://www.nextcard.com/index6.html?ref=aff0074521 PayPal is the FAST FREE and SECURE way to send money! - https://secure.paypal.x.com/refer/pal=profdredd%40yahoo.com __________________________________________________ Do You Yahoo!? Get email at your own domain with Yahoo! Mail. http://personal.mail.yahoo.com/?.refer=text - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail cbm-hackers-request@dot.tml.hut.fi.
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