A82: Interrupt speed


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A82: Interrupt speed




Hi,

Does anyone know the correct interrupt speed for the TI-82?

I made a little program and found out what you read below, any comments? The core of the program is a 26 T-states long loop run with the 4 different speed settings.

When I run it on my emulator with speed control (you'll get that version too soon) I get the values below.
The period is number of T-states between each interrupt and the number of T-states inside the interrupt routine is calculated. The differences are probably just measurement errors.

Period		Loops		Interrupt routine T-states
10000		365		510
20000		750		500
30000		1134		516
40000		1519		506
50000		1903		522
60000		2288		512

--> average interrupt routine T-states = 511

The speed (here in binary) is written to bits 1 & 2 of ports 4.
The old and new are two different set of batteries and the period is calculated.

Speed	Old		New		Old period		New period
00		441		457		11977				12393
01		1055		1092		27941				28903
10		1670		1729		43931				45465
11		2286		2364		59947				61975

This suggests a period of about 62000 T-states on fresh batteries.
Another interesting thing is that the period gets lower when the CPU runs slower. The blink rate of the cursor is probably constant no matter how bad batteries the calculator have.

If the calculator runs at 6 MHz and the interrupt period is 62500 there are 96 interrupts each second, which might be the magic value for fresh batteries - or?

Sincerely,
                       -/- David Eriksson -/-

CalcEm - The Calculator Emulator  ->  http://www.2goodsoft.com/calcem/