View source for 83Plus:Ports:21

[[Category:83Plus:Ports:By_Address|21 - Hardware Type]]
[[Category:83Plus:Ports:By_Name|Hardware Type]]
[[Category:83Plus:Ports:By_Address:Protected|21 - Hardware Type]]
== Synopsis ==
'''Port Number:''' 21h

'''Function:''' Hardware Type

This port is simply a protected register which is set by the boot code according to the hardware version.

=== Read Values ===
* Bit 0: 1 on either the 83+ SE or the 84+ SE, 0 on the 84+ basic.
* Bit 1: ''Unknown -- always set to zero''
* Bits 2-7 do not seem to do anything.

=== Write Values ===
* [00h - FFh]: New value for the register

== Comments ==
This port does not exist on the standard 83+.  See [[83Plus:Ports:02|port 2]].

There is no reason to write to this port, but by reading from it you can determine something about the HW version.

TIOS polls both bits 0 and 1, by taking the logical AND with 3.

== Example ==
 	in a,[[83Plus:Ports:02|(2)]]
 	ld b,a
 	and 80h
 	jr z,TI83p_BE
 	in a,(21h)
 	and 3
 	jr z,TI84p_BE
 	bit 5,b
 	jr z,TI83p_SE
 	; calculator is an 84+ SE
 
 TI84p_BE:
 	; calculator is an 84+ BE
 
 TI83p_SE:
 	; calculator is an 83+ SE
 
 TI83p_BE:
 	; calculator is an 83+ BE