program

Hex	80	40	20	10	08	04	02	01	Strobe DB-25 > PTS	7442 DB-25 > Pin	CD4515 DB-25 > Pin
DB-25 Pin #	9	8	7	6	5	4	3	2		17 > 12	17 > 22
100 Mhz 10 Mhz	45	49	44	43	41	40	16	15	17 > 23	16 > 13	16 > 21
1 Mhz 100 Khz	20	19	18	17	27	26	2	1	16 > 24	14 > 14	14 > 3
10 Khz 1 Khz	29	28	4	3	31	30	6	5	14 > 25	1 > 15	1 > 2
100 Hz 10 Hz	33	32	8	7	35	34	10	9	1 > 46
1 Hz 0.1 Hz	37	36	12	11	39	38	14	13	? > 47

Lets assume we want to program (123 . 456 789 1) Mhz. So how do we get all those digits out the printer port?

You will notice many parallel connections in the above chart. What I did was parallel the inputs so the same data feeds each decade in the PTS. So one has the same data going to the 100/10 Mhz digit as what is going to the 1 Mhz/100 Khz, 10 / 1 Khz, 100 / 10 Hz, and 1 / 0.1 Hz digits. So how does the PTS know what data to send where?

The secret is the strobe lines! The PTS will ignore everything at the input terminals until the corresponding strobe signal goes high. You will notice a separate strobe signal line for the 100/10 Mhz, 1 Mhz / 100 Khz, 10 / 1 Khz, 100 / 10 Hz, and 1 / 0.1 Hz digits. Each one of these digits requires four wires to send the data. There are 12 output lines available on a standard IBM printer port. 8 of these lines are used at a time to output the data. Four wires go to one digit on the PTS with the remaining four feeding the next digit.

So the first order of business is to output the 100 Mhz digit and the 10 Mhz Digit. In the above example (123 . 456 789 1) the 100 Mhz digit is a one. So we need to output binary 0001 for this digit. The 10 Mhz digit is 2. We need to output binary 0010 for this digit. BUT, we are going to output BOTH digits simultaneously. This means the 0001 has to be shifted 4 places to the left to make room for the 0010. So the output looks like this 0001 0010.

Once this data is on the output port, the corresponding strobe signal is taken high then low. In this case this would be pin 23 on the PTS. If you are using a decoder you need to send it the proper 4 bit code to cause the correct pin to go high. When you are done with this digit REMEMBER to send the proper code to take the strobe signal low again. When the strobe goes low the data is latched into the PTS and those digits associated with that particular stobe line will ignore any future transistions on the data lines.

One remaining problem! (And you thought we were done!) The PTS uses NEGATIVE TRUE LOGIC. So what does that mean? Very simple. Turn everything upside down so 0001 0010 becomes 1110 1101 before you send it out the printer port.

This process is then repeated for the 1 Mhz / 100 Khz, 10 / 1 Khz, 100 / 10 Hz, and 1 / 0.1 Hz digits