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]]
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[[Category:83Plus:Ports:By_Address:Protected|21 - Flash Size / RAM Size]] [[Category:83Plus:Ports:By_Address|21 - Flash Size/ RAM Size]] [[Category:83Plus:Ports:By_Name|Flash Size/ RAM Size]]
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{{SE-Only Port|01}}
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{{Protected Port}}
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== Synopsis ==
 
== Synopsis ==
 
'''Port Number:''' 21h
 
'''Port Number:''' 21h
  
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'''Function:''' Hardware Type
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'''Function:''' Flash Size / RAM Size
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+
−
This port is simply a protected register which is set by the boot code according to the hardware version.
+
  
 
=== Read Values ===
 
=== Read Values ===
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* Bit 0: 1 on either the 83+ SE or the 84+ SE, 0 on the 84+ basic.
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* Bits 0-1: Set flash chip size (see below)
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* Bit 1: ''Unknown -- always set to zero''
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* Bits 4-5: Set RAM chip size (see below)
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* Bits 2-7 do not seem to do anything.
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=== Write Values ===
 
=== Write Values ===
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* [00h - FFh]: New value for the register
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* Bits 0, 1, 4, 5: set new values for these bits.
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* 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]].
  
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There is no reason to write to this port, but by reading from it you can determine something about the HW version.
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The value of this port is initialized by the boot code. On the TI-83+SE, TI-84+, and TI-84+SE, bit 0 can be used to determine the hardware type alone. On the TI-84+CSE, use bits 1 and 0. If want to run on the TI-83+SE through TI+84+CSE for some reason, check both bits. The OS likes to check both bits by doing AND 3.
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=== Flash Chip Size ===
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The lower nibble controls the flash chip type. See also [[83Plus:Memory_Mapping]]. Flash pages have three different properties determined by this port: readable/censored, privileged/unprivileged, and mutable/immutable. The only censored page is the certificate page. Privileged pages can unlock flash via [[83Plus:Ports:14|port 14]]. Immutable pages cannot be written to even when flash is unlocked.
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{|-
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|<u>Value</u>&nbsp;&nbsp;&nbsp;
 +
|<u>Chip Size</u>&nbsp;&nbsp;&nbsp;
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|<u>Boot Page(s)</u>&nbsp;&nbsp;&nbsp;
 +
|<u>Certificate</u>&nbsp;&nbsp;&nbsp;
 +
|<u>Privileged</u>&nbsp;&nbsp;&nbsp;
 +
|<u>Immutable</u>&nbsp;&nbsp;&nbsp;
 +
|-
 +
|0
 +
|1024 K
 +
|3F
 +
|3E
 +
|2C-2F & 3C-3F
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|2C-2F & 3F
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|-
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|1
 +
|2048 K
 +
|7F
 +
|7E
 +
|6C-6F & 7C-7F
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|6C-6F & 7F
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|-
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|2
 +
|4096 K
 +
|FF
 +
|FE
 +
|EC-EF & FC-FF
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|EC-EF & FF
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|-
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|3
 +
|8192 K
 +
|1FF
 +
|1FE
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|1EC-1EF & 1FC-1FF&nbsp;&nbsp;&nbsp;
 +
|1EC-1EF & 1FF
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|}
 +
 
 +
 
 +
=== RAM Chip Size ===
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The TI-83+SE had an external RAM chip. This port therefore informs the ASIC what size RAM chip is installed.
 +
 
 +
{|-
 +
|<u>Value</u>&nbsp;&nbsp;&nbsp;
 +
|<u>Chip Size</u>&nbsp;&nbsp;&nbsp;
 +
|-
 +
|0
 +
|32K
 +
|-
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|1
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|64 K
 +
|-
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|2
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|128 K
 +
|-
 +
|3
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|256 K
 +
|-
 +
|}
  
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TIOS polls both bits 0 and 1, by taking the logical AND with 3.
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The actual execution permissions of RAM pages are masked by this port. Because TI sets it 0 (instead of 2), the ASIC thinks there's 32 K of RAM, and allows execution on all odd-numbered pages, instead of just 81h like TI intended. (If you set this to 1, 2, or 3, execution is also allowed on the first 1024 bytes of each page immediately following an allowed page because TI screwed up on [[83Plus:Ports:26#Comments|port 26h]].) If you ever attempt to execute code from a non-executable page, the calculator resets.
  
 
== Example ==
 
== Example ==

Latest revision as of 17:32, 20 February 2013

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: Flash Size / RAM Size

Read Values

  • Bits 0-1: Set flash chip size (see below)
  • Bits 4-5: Set RAM chip size (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. On the TI-83+SE, TI-84+, and TI-84+SE, bit 0 can be used to determine the hardware type alone. On the TI-84+CSE, use bits 1 and 0. If want to run on the TI-83+SE through TI+84+CSE for some reason, check both bits. The OS likes to check both bits by doing AND 3.

Flash Chip Size

The lower nibble controls the flash chip type. See also 83Plus:Memory_Mapping. Flash pages have three different properties determined by this port: readable/censored, privileged/unprivileged, and mutable/immutable. The only censored page is the certificate page. Privileged pages can unlock flash via port 14. Immutable pages cannot be written to even when flash is unlocked.

Value    Chip Size    Boot Page(s)    Certificate    Privileged    Immutable   
0 1024 K 3F 3E 2C-2F & 3C-3F 2C-2F & 3F
1 2048 K 7F 7E 6C-6F & 7C-7F 6C-6F & 7F
2 4096 K FF FE EC-EF & FC-FF EC-EF & FF
3 8192 K 1FF 1FE 1EC-1EF & 1FC-1FF    1EC-1EF & 1FF


RAM Chip Size

The TI-83+SE had an external RAM chip. This port therefore informs the ASIC what size RAM chip is installed.

Value    Chip Size   
0 32K
1 64 K
2 128 K
3 256 K

The actual execution permissions of RAM pages are masked by this port. Because TI sets it 0 (instead of 2), the ASIC thinks there's 32 K of RAM, and allows execution on all odd-numbered pages, instead of just 81h like TI intended. (If you set this to 1, 2, or 3, execution is also allowed on the first 1024 bytes of each page immediately following an allowed page because TI screwed up on port 26h.) If you ever attempt to execute code from a non-executable 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
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