Difference between revisions of "83Plus:Ports:29"

Revision as of 20:15, 4 April 2005

Synopsis

Port Number: 29h

Function: LCD Speed (6 MHz)

This port controls the calculator's LCD speed when it is running at 6 MHz. It is complicated and the lower four bits have not been thoroughly investigated but should be 7h on the TI-83/84 Plus Silver Edition at all times.

Values

Setting bits 4-7 on this port has the effect of shortening the required LCD delay. Bits 7-5 control the removed delay in powers of 2 (i.e. setting bit 7 removes 1/2 of the original delay, setting bit 6 removes 1/4, and bit 5 1/8). Bit 4 is related to bits 7-5 by a factor of 3/26. If the entire upper nibble of port 29h is zero, the LCD will not update.

The formula below calculates the amount of delay removed by setting bits 7-4 (the lower nibble of the port should always be 7). b7, b6, b5, b4 are either 0 or 1 and represent the value of their corresponding bit.

Percentage of delay removed [0-1] = (b7/2) + (b6/4) + (b5/8) + (3/26)(b7)(b4) + (3/52)(b6)(b4) + (3/104)(b5)(b4).

Note however if port 29h is set to 27h, then the % of delay removed is actually (1/8) - (3/104).

For a simple table of common values:

Value     Relative speed (100% is normal, 200% would mean the LCD is twice as fast)
17      100%
27      110%
47      133%
67      160%
87      200%
A7      267%
C7      400%
E7      1300%
F7      1600%

Comments

This port is not available on the normal TI-83+. On the normal TI-83+ this port is a shadow of Port 09h.

Credits and Contributions

• Michael Vincent: Documentation as found here.