Strange behavior of #8 button
|
Ah; that may be a hint. The Z80MC runs *cold". Everything is CMOS, nothing gets hot.
What are you using for a power supply? Could its voltage be insufficient? USB supplies are often weak, and the cables so thin that they have lots of voltage drop. I haven't seen this problem with the Z80MC (which draws less than 100mA), but it often happens with the Altaid 8800 (which draws close to 500mA). Lee -- Excellence does not require perfection. -- Henry James But it *does* require attention to detail! -- Lee Hart -- Lee A. Hart |
|
I cannot get S8 work no matter what. While running FFF1 sequence it is using 92mA current at 5V supply.? While testing with the logic probe, 74LS145 inputs to A(15), B(14) and C(13) are fine but D(12) is always LOW. I am using the (b) TTL configuration both on the Z80 card as well as the Front panel. On Fri, Mar 28, 2025 at 4:04?PM Lee Hart via <leeahart=[email protected]> wrote: Ah; that may be a hint. The Z80MC runs *cold". Everything is CMOS, nothing gets hot. |
|
> I cannot get S8 work no matter what. While running FFF1 sequence it is using 92mA current at 5V supply. ? OK, that's correct. You have enough 5v power. ? > While testing with the logic probe, 74LS145 inputs to A(15), B(14) and C(13) are fine but D(12) is always LOW. ? That's also correct. 74LS145 input D (pin 12) is always low when the interrupt handler is working. The inputs to it count from 0-7 and repeat. If the Z80 interrupt handler fails to respond to the keyboard/display interrupt, then input D (pin 12) goes high to disable the LED display and keypad. ? As I described earlier, you can test the Front Panel by itself, without the CPU board. You should be able to set the A B C inputs of the 74LS145 (with the 74HC393 counter) to each of the 8 states, then operate each keypad key in turn, and see the IN bits identify which key you pressed. ? Lee ? I am using the (b) TTL configuration both on the Z80 card as well as the Front panel. -- Excellence does not require perfection. -- Henry James But it *does* require attention to detail! -- Lee Hart -- Lee A. Hart |
|
Here is the recommended setup for standalone testing of the front panel, just to make sure it is the correct start. -J2 Pin 9 [/out] is connected to 3 components. 0.1uF cap other end ground, momentary switch other end ground, 100K resistor other end Vcc(5V). Original recommendation was to use J2 Pin 8, however (b)TTL option that pin is not connected to anything but P1 TX 5. -J2 Pin 24 -CLOCK- high (Vcc) or low (Ground) -P1 1 ground to (-) power supply -J2 P19 Vcc to +5V power supply On Fri, Mar 28, 2025 at 5:01?PM Lee Hart via <leeahart=[email protected]> wrote:
|
|
Kerem Kapkin wrote: > Here is the recommended setup for standalone testing of the front panel... > J2 Pin 9 [/out] connected to 3 components. 0.1uF cap other end ground, > momentary switch other end ground, > 100K resistor other end Vcc(5V). ? Correct. This provides a debounced pushbutton to clock counter U2A. ? > J2 Pin 24 -CLOCK- high (Vcc) or low (Ground) ? Either is fine; you just don't want to leave a CMOS input floating. ? > P1 pin 1 ground to (-) power supply ? Or J2 pin 10 also works. ? > J2 Pin 19 Vcc to +5V power supply ? With this setup, you can step counter U2A through its states 0-7. Each state is output on J2 pins 11, 12, and 13. Each state should set the corresponding output of U3 low so you can test each button. ? I think I see the problem with the "8" key! When U3 output C0 is low, IN4 (J2 pin 15) should be high. But transistor Q3 is also connected to C0. It is a "pre-biased" FJN3305, which has internal 10k and 4.7k resistors between its base and emitter. Its emitter ties to C0, and its base to R1D, a 1.5K to ground.These three resistors (10K + 4.7K + 1.5K = 16.2K) are pulling C0 low despite 18K R4A trying to pull it high! Thus the "halfway between" logic level, on IN4. ? I'm busy preparing for VCF-East right now, but will confirm this when I return. In the meantime, I'll bet putting a lower value resistor (like 1.5K) in parallel between R4A pins 1-2 will fix the problem. Lee -- Excellence does not require perfection. -- Henry James But it *does* require attention to detail! -- Lee Hart -- Lee A. Hart |
|
Thanks Lee, a 22K resistor in parallel with R4 A between pins 1 and 2 solved the problem with S8. On Sat, Mar 29, 2025 at 11:52?AM Lee Hart via <leeahart=[email protected]> wrote:
|
|
I originally used FJN3303 transistors, which have internal 22k+22k resistors. When Mouser stopped stocking the thru-hole versions, I had to switch to FJN3305 with internal 4.7k+10k resistors. I *thought* they worked OK. Obviously I was wrong! ? Since then, I bought some FJN3304 transistors with 47k+47k for my 1802MC. I'm going to try them in the Z80MC Front Panel to see if they are a better choice. If so, it's an easy change. :-) ? (An aside: Lots of manufacturers still make these pre-biased transistors. But a) they don't provide thru-hole versions any more, and b) instead of assigning 2Nxxxx numbers to facilitate 2nd sources, they hide them under house numbers.) ? Lee -- Excellence does not require perfection. -- Henry James But it *does* require attention to detail! -- Lee Hart -- Lee A. Hart |
|
Now that the Front Panel is working, I need to fix the SIO card which I think accidentally destroyed during the troubleshooting of the Front Panel. SIO card received 9V instead of 5V now all LEDs are on and no response from the board. So I am guessingthat I fried the 74LS259 bit latch which has a max Vcc 5.5 unlike the 74HC, and directly connected to the LEDs. Next would be to replace 74LS01, however I only have a 74LS03 that won’t work.? |
|
Thanks Allison. I have replaced the 74SL259 with a new one, but didn’t make any difference. On Mon, Mar 31, 2025 at 8:39?AM ajparent1/kb1gmx via <kb1gmx=[email protected]> wrote:
|
Lee Hart
Kerem Kapkin