Difference between revisions of "83Plus:Ports:21"
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| − | [[Category:83Plus:Ports:By_Address:Protected|21 - Hardware Type]] [[Category:83Plus:Ports:By_Address|21 - Hardware Type]] [[Category:83Plus:Ports:By_Name|Hardware Type]] | + | [[Category:83Plus:Ports:By_Address:Protected|21 - Hardware Type / RAM Protection]] [[Category:83Plus:Ports:By_Address|21 - Hardware Type / RAM Protection]] [[Category:83Plus:Ports:By_Name|Hardware Type / RAM Protection]] |
{{SE-Only Port|01}} | {{SE-Only Port|01}} | ||
{{Protected Port}} | {{Protected Port}} | ||
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'''Port Number:''' 21h | '''Port Number:''' 21h | ||
| − | '''Function:''' Hardware Type | + | '''Function:''' Hardware Type / RAM Protection |
| − | This port is | + | This port is used as a flag to identify the hardware type (TI-84+ basic versus SE), as well as controlling the RAM execution protection. |
=== Read Values === | === Read Values === | ||
* Bit 0: 1 on either the 83+ SE or the 84+ SE, 0 on the 84+ basic. | * Bit 0: 1 on either the 83+ SE or the 84+ SE, 0 on the 84+ basic. | ||
* Bit 1: ''Unknown -- always set to zero'' | * Bit 1: ''Unknown -- always set to zero'' | ||
| − | * Bits | + | * Bits 4-5: current RAM protection mode (see below) |
=== Write Values === | === Write Values === | ||
| − | * | + | * Bits 0, 1, 4, 5: set new values for these bits. |
| + | * Bits 2, 3, 6, 7: ignored | ||
== Comments == | == Comments == | ||
This port does not exist on the standard 83+. See [[83Plus:Ports:02|port 2]]. | This port does not exist on the standard 83+. See [[83Plus:Ports:02|port 2]]. | ||
| − | + | The value of this port is initialized by the boot code to either 01 (TI-83+ SE, TI-84+ SE) or 00 (TI-84+ basic.) Bit 0 can thus be used to determine the hardware type (in fact, the OS checks both bits 0 and 1, by ANDing the value with 3; it may be a good idea for user programs to do the same.) | |
| − | + | === RAM protection modes === | |
| + | There are four possible RAM protection modes, which have differing effects in terms of which RAM pages are permitted to contain executable code. Note that bits 4-6 of the page number are ignored for purposes of determining executability (e.g., page 92h is equivalent to page 82h.) | ||
| + | |||
| + | * '''Mode 0''' (the default): Execution is allowed on pages 81h, 83h, 85h, 87h, 89h, 8Bh, 8Dh, and 8Fh. | ||
| + | * '''Mode 1''': Execution is allowed on pages 81h, 82h, 85h, 86h, 89h, 8Ah, 8Dh, and 8Eh. | ||
| + | * '''Mode 2''': Execution is allowed on pages 81h, 82h, 89h, and 8Ah. | ||
| + | * '''Mode 3''': Execution is allowed on pages 81h and 82h only. | ||
| + | |||
| + | (If you ever attempt to execute code from a "disallowed" page, the calculator resets.) | ||
== Example == | == Example == | ||
Revision as of 18:45, 30 September 2009
| This port only exists as a distinct port on the TI-83 Plus Silver Edition, the TI-84 Plus, and the TI-84 Plus Silver Edition. On the standard TI-83 Plus, it acts as a shadow of port 01. |
| This port is protected, which means user programs cannot ordinarily write to it directly. |
Synopsis
Port Number: 21h
Function: Hardware Type / RAM Protection
This port is used as a flag to identify the hardware type (TI-84+ basic versus SE), as well as controlling the RAM execution protection.
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 4-5: current RAM protection mode (see below)
Write Values
- Bits 0, 1, 4, 5: set new values for these bits.
- Bits 2, 3, 6, 7: ignored
Comments
This port does not exist on the standard 83+. See port 2.
The value of this port is initialized by the boot code to either 01 (TI-83+ SE, TI-84+ SE) or 00 (TI-84+ basic.) Bit 0 can thus be used to determine the hardware type (in fact, the OS checks both bits 0 and 1, by ANDing the value with 3; it may be a good idea for user programs to do the same.)
RAM protection modes
There are four possible RAM protection modes, which have differing effects in terms of which RAM pages are permitted to contain executable code. Note that bits 4-6 of the page number are ignored for purposes of determining executability (e.g., page 92h is equivalent to page 82h.)
- Mode 0 (the default): Execution is allowed on pages 81h, 83h, 85h, 87h, 89h, 8Bh, 8Dh, and 8Fh.
- Mode 1: Execution is allowed on pages 81h, 82h, 85h, 86h, 89h, 8Ah, 8Dh, and 8Eh.
- Mode 2: Execution is allowed on pages 81h, 82h, 89h, and 8Ah.
- Mode 3: Execution is allowed on pages 81h and 82h only.
(If you ever attempt to execute code from a "disallowed" page, the calculator resets.)
Example
in a,(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
