On Sun, 1 Apr 2001, [ISO-8859-1] Marko Mäkelä 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 29_lv_160. Try looking for a straight 29160 ;) the 'lv' indicates its a 3.3v part > 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. The gameboy color mega cart flash rom is a 2meg part, and has to be 5v, given its target platform > > 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 firstname.lastname@example.org. > - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail email@example.com.
Archive generated by hypermail 2.1.1.