Jan. 23, 1977
DEPARTMENT OF PHYSICS
Jan. 23, 1977
Mr. J. Torzewski
51625 Chestnut Road
Granger, IN 46530
Dear Mr. Torzewski:
I can give only partial answers to your questions, and it has taken me
some time to assemble this much information. We did not make the conversion to
16K memory chips. That was done by Steve Jobs of Apple Computer, and he did not
give us any documentation. Therefore, I have taken photos of the board to show
the connections, and these are enclosed.
In the breadboard area, there are five sockets. One of them (slides 13
and 15: at the left if breadboard area is at the top) is a socket for the flat
cable connecting to the SWTP printer. The next small socket and the large one
were for a project that was never completed, and so have no function. The two
on the right, labelled 74153 and 74139, are for integrated circuits with those
part numbers and are used in the 16K chips conversion. The connections to these
sockets are the light green wires shown in slides 17 and 19. Note that two
traces on the underside of the board have been cut for the 16K conversion. They
have been bridged by the red wires shown in the photograph. Also, the X-0
solder bridge in the chip select area must be cut. (The red wires in that area
were for another unfinished project and serve no useful function). Pin 14 of
integrated circuit 74S257 at location B-8 was bent so that it did not go into
the socket. If you have questions about the photograph and can't see where a
particular wire goes, we can look again at our board, but this is about all we
Steve Jobs published an article describing how to interface to an STWP
printer, in the October 1976 issue of Interface Age. A copy of that article is
enclosed. We followed it, and the corresponding connections are the yellowish
green and red-white wires shown in slide 17. There is a switch to permit the
computer to output characters to the TV display when the printer is not in use.
It is indicated in Jobs' article and is mounted on the comptuer hoiusing so that
it is not visible in these photos.
I am enclosing a handwritten sheet listing some of the commands of the
extended monitor, a copy of the commands of the Apple II monitor, and a
disassembler listing of the extended monitor. Frankly, I believe that the
extended monitor was juast a design study for the Apple II, and it is not much use
for the Apple I especially if you have only 8K memory.
I hope to hear something of what you have been learning before too long.
Would it be worthwhile for you to start a newsletter and sell subscriptions?
Arthur L. Schawlow