We are making good progress on the clock, the hardware at least. I'm going to build it all on the breadboard first.
Here are the breadboard photos:
http://www.vintage-computer.com/vcforum/album.php?albumid=300&attachmentid=27064
http://www.vintage-computer.com/vcforum/album.php?albumid=300&attachmentid=27065
I have the six general purpose output bits going two places. For status indication, they go to a 74240 acting as a buffer driver for eight LEDs. AM/PM each have their own LEDs, but are driven by one bit and are mutually exclusive. Similarly I have date/time each with their own LED from one bit, also mutually exclusive. The others indicate a "setup" mode, alarm 1 active, alarm 2 active, and the last bit will eventually drive an alarm beeper, but is on an LED now.
The second place the six output bits go is to a 74125 binary to BCD. One 74125 can yield 7 bits of BCD. The low 4 bits drive one 7447, and the high three a second 7447. The low and high 7447s each drive all three high digits and low digits of two digit seven segment displays. The cathodes of each pair of displays can be strobed to make that pair active through a 2N3906. Obviously there is a pair of digits for hours(month), minutes(day), and seconds(year). Thank goodness there are six bits, so that we can count to at least 59 minutes, or 63 years. (Yes, this clock will have a problem in the year 2064. The six bits will only allow the years counter to count to [20]63. I will worry about this problem then, if I'm still alive.)
As Pete suggested, the IO3CS through IO6CS lines on J5 are used as strobes. One each for the status LEDs on the 74240 through the enable, and the pairs of digits through their 2N3906s. The IOxCS lines drive clock inputs of 7473s that are setup to toggle the Q or not Q outputs as approriate. Addressing 166000, 170000, 172000, or 174000 by doing a write generates a pulse on the associated IOxCS line, causing the associated JK flop to toggle and either light or extinguish that digit pair or the status LEDs.
So at any given time, the six general purpose output bits either have status info, or have the hour/month/minute/day/seconds/year value. I expect to be able to use persistence of vision to strobe fast enough so that a viewer can't tell that only one pair of digits or the status LEDs are truly lit at any instant in time.
For clock setting input, I have three pushbuttons debounced with 7414 schmitt trigger inverters to three of the four general purpose input bits. The fourth bit will be the 1 Hz signal from the RED60, which I have not installed yet, but it is next.
All of the above works properly. I have exercised it extensively in the immeadiate mode of the Forth interpreter.
I measured the current of all this stuff so far at 580mA. For the permanent power supply, I plan to use a small 6.3V center tapped transformer with two diodes, a 7805, and approriate input and output filtering. The RED60 will take the unrectified AC from the transformer secondary as input. The RED60 1Hz output will feed the fourth general purpose input bit. *** 10/9/15 edit - this is all now installed and tested :
http://www.vintage-computer.com/vcforum/album.php?albumid=300&attachmentid=27082
The software should be simple, but it will be my first "practical" work in Forth. More to come.....
Lou
PS. a little trick I found to connect male breadboard jumper wires to male header pins was to use header jumper plugs. One port of the jumper plug goes on the header pin while the other port receives the breadboard jumper wire.