> 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. > Are you familiar with latchup? Parasitic SCRs that switch on and short the device under certain conditions (like when the protection diodes are passing enough current). I don't know how much of a problem this might be in modern devices, especially ones designed to operate in mixed voltage environments. I note that that link you posted say "latchup performance exceeds 300ma" not sure what that means, either that you must inject >300ma to cause latchup, or the SCR holding current exceeds 300ma (I'm guessing) I also note that it says "do not force a signal on an I/O pin when it is an active output, damage may occur" I suspect trying to drive a 5V line would be included there. I know I've read several app notes on the subject, I'll see if I can find them, if you're interested. (not sure if they were on line or in an electronic form) > 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 > Is the circuit viewable somewhere? bogax - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail firstname.lastname@example.org.
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