LED Clock: Enough Controller Pins?

Last night, while programming the LogoChip A6276 interface, I started to become concerned about having enough LogoChip pins to connect to everything I want to wire up to make the clock work. So I just did a quick sanity check to see whether I’ll have enough pins, or whether I need to double up digits together.

Here are the LogoChip pins:

Available Pins
A0 – A2
A3 – A5 ?
B0 – B7
C6 – C7

I’m not sure whether A3 – A5 are available or not. They’re ghosted (grey) on the LogoChip sticker, and I’m not sure why. But because of that, I think I didn’t provide sockets for them on my Curiously Strong LogoChip, which may pose challenges while prototyping. Additionally, A0 – A2 didn’t work for driving the 6276, so maybe not even all of the available pins will work.

Anyway, here’s a tentative pin assignment.

Chip Lines Count Possible LogoChip Lines
A6276 LED driver serial data in
latch (each character)
A0 – A1 (didn’t work)
   or B0 – B1
B0/2 – B8
Dallas clock chip data
2-3 A0 – A2 (didn’t work for A6276)
PC serial port? TD
2 C6 – C7

[Ewww, I don't like what the WordPress stylesheet does to the table text alignment.]

Looks like everything should work out, assuming that I can use all the pins the way I intended. In fact, if the clock is only six digits, I can use B0 – B1 for the 6276 data and clock lines and B2 – B7 for the digits’ latch lines, fitting the entire display driver into one I/O port. Tidy.

The Dallas timekeeping chip will need either two or three pins, depending on whether I use the DS1340 with I2C or the DS1302 with “simple” three-wire interface.

The LogoChip already connects to the PC’s serial port on pins C4 and C5; however, receiving data halts a running program. That means that while uploading control data to the LogoChip, although the real-time clock chip would continue to keep time, the display would freeze and stop updating; and that every data transmission would need to be followed by a command to restart the display program.

Since I may want to be able to send updates to the LogoChip while it’s operating (time corrections, commands to change display mode, etc.), I’m thinking of using the PIC’s built-in UART on C6 and C7 for run-time serial communication.

Anyway, the bottom line is that as long as I can figure out how to use the A port lines for digital I/O, and as long as we’re only making a six-character clock (HH:MM:SS without .TH), there are enough lines. Good deal.

One Response to “LED Clock: Enough Controller Pins?”

  1. Muaz says:

    Interesting to see what you’re up to. Hope you’re having better luck with the driver chips… They’re not terribly difficult to work with. My code wasn’t as complicated but I was able to pin point and light any specific LED I want using only the drivers and minimal outputs from the LogoChip. Of course, I had three 16-bit drivers which expanded the number of LEDs I could use and control. I have found that the output enable pin is very handy, especially to avoid ghosting. Your project should concentrate more on the software rather than the hardware, I think.

    I hate Port A of the LogoChip. It must have something to do with the analog inputs. Have you tried disabling them?

    Good luck!!

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