Zeroko: Based on 83Plus:Ports:01, changed key labels & added battery level

2021-09-20T19:47:19Z

Based on 83Plus:Ports:01, changed key labels & added battery level

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[[Category:86:Ports:By_Address|01 - Keyboard]] [[Category:86:Ports:By_Name|Keyboard]]
== Synopsis ==
'''Port Number:''' 01h

'''Function:''' Keyboard Port

This port reads key presses from the keypad. The keypad is divided into a series of groups.

See also [[83Plus:Ports:01|TI-83 Plus Port 01]], which is identical apart from the key labels & the lack of battery level detection.

=== Read Values ===
* Bits are set according whether corresponding keys from selected groups are pressed. Groups are selected through writing to the port. A pressed key reads a 0 bit. An unpressed key reads a 1 bit.
* Bit 0 will also read as 0 if groups 0-2 are all selected & the battery level is low.

=== Write Values ===
* FFh : Reset the keypad. This unselects all groups and resets the keypad state.
* F8h : Check battery level. This also selects keypad groups 0-2 for monitoring.
* Anything else : Any 0 bit adds the corresponding group to the list of monitored groups. When a key in a monitored group is pressed, the corresponding key bit reads 0, otherwise it reads 1 (active-low).

== Key Map ==
The key map is laid out as follows:

{|
|
! Group Bit
| 0 || 1 || 2 || 3 || 4 || 5 || 6 || 7
|-
|
! Group Mask
| FE || FD || FB || F7 || EF || DF || BF || 7F
|-
! Key Bit !! (Mask)
|-
! 0 !! (FE)
| DOWN||ENTER|| (-) || . || 0 || || F5 || ||
|-
! 1 !! (FD)
| LEFT|| + || 3 || 2 || 1 || STO || F4 || ||
|-
! 2 !! (FB)
|RIGHT|| - || 6 || 5 || 4 || , || F3 || ||
|-
! 3 !! (F7)
| UP || * || 9 || 8 || 7 || x<sup>2</sup> || F2 || ||
|-
! 4 !! (EF)
| || / || ) || ( || EE || LN || F1 || ||
|-
! 5 !! (DF)
| || ^ || TAN || COS || SIN || LOG || 2nd || ||
|-
! 6 !! (BF)
| ||CLEAR||CUSTOM||PRGM ||TABLE||GRAPH||EXIT || ||
|-
! 7 !! (7F)
| || || || DEL ||x-VAR||ALPHA||MORE || ||
|}

* '''Note:''' Group FB Key FE is NEGATE, not to be confused with SUBTRACT.
* '''Note:''' Group DF Key FE would be ON, but the ON key is tested through [[86:Ports:03|Port 03]], bit 3.

== Comments ==
* The OS delays about 1400 cycles (100 iterations of a tight DJNZ loop) when checking the battery level at startup, which is much longer than used to test if keys are pressed.
* Bit 0 will be 0 when testing the battery level if the warning message would appear. However, because it is still also wired to the keypad, holding any of DOWN, ENTER, or (-) when turning the calculator on will also cause the warning message to appear.

86:Ports:01 - Revision history

Zeroko: Based on 83Plus:Ports:01, changed key labels & added battery level