Computing Devices of Canada SDA103

The SDA103 is a 1975 vintage serial communications analyzer.

Mods

Modifying Preset Baud Rates

This is mainly for my own memory. The baud rate is set using a diode matrix. I wanted it to support 45.45 baud. By analyzing the existing configurations, I was able to modify the programming to change 134.5 baud into 45.45 baud.

The formula for calculating the required diode settings is:

n = (clock/200/baud)-1

Conversely,

baud = clock/200/(n+1)

Where clock can be 11.52 MHz or 11.97 MHz, whichever produces the value closest to the desired baud rate.

Row	Target Baud Rate	Crystal	A	B	C	D	E	F	G	H	J	K	L	Hex	Dec	Actual  Baud  Rate	Error
1	50	11.52 MHz	•	•	•	•	•	•	•				•	0x47F	1151	50.00	0.0000%
2	74.2	11.52 MHz	•	•	•						•	•		0x307	775	74.23	0.0361%
3	110	11.97 MHz	•	•	•	•	•					•		0x21F	543	110.02	0.0167%
4	134.5	11.97 MHz			•	•	•	•		•	•			0x1BC	444	134.49	-0.0042%
5	150	11.52 MHz	•	•	•	•	•	•	•		•			0x17F	383	150.00	0.0000%
6	300	11.52 MHz	•	•	•	•	•	•		•				0x0BF	191	300.00	0.0000%
7	600	11.52 MHz	•	•	•	•	•		•					0x05F	95	600.00	0.0000%
8	1200	11.52 MHz	•	•	•	•		•						0x02F	47	1200.00	0.0000%
9	1800	11.52 MHz	•	•	•	•	•							0x01F	31	1800.00	0.0000%
10	2400	11.52 MHz	•	•	•		•							0x017	23	2400.00	0.0000%
11	4800	11.52 MHz	•	•		•								0x00B	11	4800.00	0.0000%
12	9600	11.52 MHz	•		•									0x005	5	9600.00	0.0000%
Settings for 45.45
	45.45	11.97 MHz			•			•			•		•	0x524	1316	45.44	-0.0128%