Hey there =]

If you don't already know, a delay is needed between writing and reading to the keyboard (using port 1).
The problem is, that the needed time is not accurately known.
Since there seems to be many different opinions about the subject, i decided to code a program to test that up.
The main purpose is to be able to have a better knowledge of the hardware, allowing more optimised low level operations.
Also, maybe we'll have some surprises (ti likes to change hardware pieces).

COMPATIBILITY

TI-83 Plus
TI-83 Plus.fr
TI-83 Plus Silver Edition
TI-84 Plus
TI-84 Pocket.fr
TI-84 Plus Silver Edition
TI-84 Plus Pocket Silver Edition
TI-84 Plus C Silver Edition

All official OS are compatible, as long as you TURN OFF MATHPRINT.

INSTRUCTIONS

Simply execute from the homescreen and follow instructions.
Important : When pressing the 0 key, you must HOLD it until the end of the test.

DOWNLOAD

black & white models : http://www.omnimaga.org/index.php?action=dlattach;topic=16102.0;attach=15043
TI-84 Plus C Silver Edition : http://www.omnimaga.org/index.php?action=dlattach;topic=16102.0;attach=15044

RESULTS

The displayed value(s) are the needed delays (in cycles) for each CPU speed mode (order : 0,1,2,3).
A question mark specifies an unknown delay.
Please don't forget to specify the model and serial number end (at the back of your calc, in the form X-XXXXX).

OWNER MODEL SERIAL DELAY-0 DELAY-1 DELAY-2 DELAY-3

the_mad_joob 83+ I-0299A 6
bhtooefr 83+ S-0504E 0
chickendude 83+ N-0305H 5

fortytwo 83+SE I-0501 4 23 30 37 overclocked

Darl181 84+ S-0305B 6 29 29 29
Streetwalker 84+ S-0107G 4 21 21 21

the_mad_joob 84+SE S-0404 6 29 29 29
DrDnar 84+SE S-0605D 4 19 19 19
fortytwo 84+SE P-0410O 4 17 17 17
willwac 84+SE P-0410O 4 20 20 20
chickendude 84+SE ? 4 18 18 18

DrDnar 84+CSE ? 22 72 72 72

THANKS IN ADVANCE FOR YOUR PARTICIPATION =]

Reading such results reminds me how slow is my 84+se

Thx a lot Streetwalker !

You should ask KermM to run that on his 22 MHz TI-83+SE. (Its ASIC is a beta version of the TI-84+/C/SE ASIC.)

84PBE, S-0305B
6, 29, 29, 29.

Iirc the older calcs are slightly slower hardware-wise. There used to be a topic, but I can't seem to find it anymore..

They make up for it in ram pages and other fun tho

How on earth does someone "time" a processor with only the processor to do so?
And the same goes for keypresses! Wahh lol

It's not really timing the processor with the processor.  It's more like timing the keyboard delay with the processor clock. 

You can time the processor easily enough using only the processor:

Simply start a loop with a known number of cycles. Have it run long enough to get a decent length of time. (Say, 100 million cycles)

Simple math based on the time can tell you the processor's speed in Hz.

Yes, there is a problem with your source code. You forgot to disable interrupts, which could cause false values to be reported.

I get {4, 19, 19, 19}. My calculator is a TA3-type unit S-0605D.

The needed wait time appears to be 1 or 2 microseconds. The keyboard circuits may involve an analog component, so external (or internal) forces could affected the needed wait time. The keyboard outputs are open-drain type, and the inputs have internal pull-up resistors. TI probably chose resistances that reduce power usage, which has the side effect of requiring longer wait times before keyboard matrix output transistors settle.

How on earth does someone "time" a processor with only the processor to do so?
And the same goes for keypresses! Wahh lol
Should I test different OS versions?

We're measuring time from the point of view of the processor itself, so we don't need an external reference. We also have more than only the processor: the so-called crystal timer circuits can not only measure time in terms of the 32768 quartz crystal (which I use in my CPU clock frequency tester), but the circuits can also measure time in terms of the CPU clock divided by any of 8 different constants.