|
|
 
There are 12 parts to this article:
1 -
2 -
3 -
4 -
5 -
6 -
7 -
8 -
9 -
10 -
11 <
12
There are 6 Z-80 PIOs used to communicate with the outside world. The PIOs are numbered 0-5 on the schematic. PIO-0 is hooked up to the LED display. Eight bits select the LED to latch, and eight bits supply the data. The drivers for the LEDs are simply 74LS374s and 74LS244s. PIO-1 and PIO-2 hook up to the incandescent lamps. The five outgoing lines to the PC parallel port also hook up to the lower five bits on PIO-2-A. The nine incoming lines from the PC parallel port go to PIO-3-A and PIO-4-5. PIO-4-B-0-2 are used for the status incandescent lamps. PIO-4-A-0-5 are used for the keypad, which is just a binary keypad using a 74C922. Referring to the schematic, all of the other lines are I/O lines.
The reset and memory select switches electrically just go to ground when closed.
To sink enough power to get the incandescents to light correctly (it has been ten years, so I'm guessing) the common is 14 volts. There are transistors (2n2222s) with 3.4K (2 6.8K in parallel) resistors going to the PIO ports for each lamp. Related, I'm sure, is the quirk that the reset and memory select switches actually turn on 2n2222s using a 10k resistor. That is, the switches switch 14 volts, which then grounds out the mem/reset line.
Here are the details of the PC Printer Port connection:
2-3a0-O(ut from PC)
3-3a1-O
4-3a2-O
5-3a3-O
6-3a4-O
7-3a5-O
8-3a6-O
9-3a7-O
10-2a3-I(n from PC)
11-2a4-I
12-2a2-I
13-2a1-I
15-2a0-I
17-4a5-O
25-Ground from PC
|
Here is a summary of the other two DB-25 ports:
Keyboard port:
1 4a0
2 4a1
3 4a2
4 4a3
5 4a4
6
7
8
9 +5
10
11
12 GND
13
14
15
16
17
18
19
20
21
22
23
24
25
Expansion 1 port:
1
2
3
4
5
6 3b7
7 3b6
8 3b5
9 3b4
10 3b3
11 3b2
12 3b1
13 3b0
14 4b7
15 4b6
16 4b5
17 4b4
18 4b3
19
20
21
22
23 4a7
24 4a6
25
|
There is another PIO (5) that has terminal strips hooked up, and is used in this article.
|
|
