I believe that is how the PET is, since the BASIC test routine worked on the Plus/4. Good thing I am testing, found some BASIC bugs from the OCR of the listing... and for some odd reason I could not define the variable "port" on either the plus/4 or 64... never run into that one before... I have verified the pinout (The plus/4 always seems to amaze me in it's 'different similarities').. Talk about tight squeeze, I had to file off a millimeter or so off the side edges of the user port opening to get the connector to fit. Next comes the VIC-20 and hopefully the P-500. Richard Atkinson wrote: > > On Mon, 24 Jul 2000, William Levak wrote: > > > > but I cannot find an entry for the cooresponding Data Direction Register > > > which assigns the bits as input or output.... :/ > > > > There isn't one. This is a 6529 single port interface (data sheet on > > funet). When you read that address, all 8 data lines are read. When you > > write, all 8 data lines are written. > > In a sense, the data register also acts as a data direction register. When > you write a zero to a bit, it becomes an output holding that line low. Any > reads from that bit will yield a zero. When you write a one to that bit, > it becomes an input and will be pulled high unless something else attached > to it is holding it low. Thus when you read from it, it is either a one or > a zero depending on the voltage on it. This is all due to open-drain > logic. It's implemented as a buffer (to read from) and a transistor / > pullup resistor pair (to write to). Reading it returns the state of the 8 > buffers and writing to it latches 8 bits into a register connected to the > transistors. > > Richard > -- 01000011 01001111 01001101 01001101 01001111 01000100 01001111 01010010 01000101 Larry Anderson - Sysop of Silicon Realms BBS (209) 754-1363 300-14.4k bps Classic Commodore pages at: http://www.jps.net/foxnhare/commodore.html 01000011 01001111 01001101 01010000 01010101 01010100 01000101 01010010 01010011 - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail firstname.lastname@example.org.
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