83Plus:Ports:02

Synopsis

Port Number: 02h

Function: Calculator Status Information

This port reports various status information, including battery strength, LCD driver status, and calculator type.

Read Values

• Bit 0: Set if the batteries are good. Reset if the batteries are low. The calculator will refuse to Garbage Collect or receive a FLASH App or OS when the batteries are low.
• Bit 1: Set if the LCD Driver can receive a command. Reset otherwise. This is basically the inverse of bit 7 from Port 10h.
• Bit 5: Set for TI-84+ and TI-84+ SE calculators. Reset for TI-83+ and TI-83+ SE calculators.
• Bit 7: Reset for a TI-83+ Basic. Set for everything else.

Write Values

• No useful effect.

Comments

See Port 21h for how to distinguish the 84+ Basic from the 84+ SE.

Example

Battery checking

 push af
 in a, (2)
 and 01h
 call nz, BatteriesGood
 call z, BatteriesLow
 pop af

LCD Testing

 push af
WaitLoop:
 in a, (2)
 and 02h
 jr z, WaitLoop
 ;Send a command, like 03 (LCD "On").
 call LCDIsReady
 pop af

Device checking

This example also uses Port 21h.

 in a, (2)
 rlca ;Roll bit 7 into carry.
 jp c, Regular83Plus
 rlca
 rlca ;Roll bit 5 into carry.
 jp nc, Silver83Plus
 in a, (21h)
 and 01h
 jp z, Regular84Plus
 jp nz, Silver84Plus

Credits and Contributions

• Michael Vincent: Documentation of port 2 located here.