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Port Number: A000-?

Memory-mapped address: F50000-?

Function: Keypad Controller


  • F50000 (R/W):
    • Bits 0-1: Scan mode
      • Mode 0: Idle.
      • Mode 1: Indiscriminate key detection. Data registers are invalid, but whenever any key is pressed, interrupt bit 2 is set (and cannot be cleared until the key is released).
      • Mode 2: Single scan. The keypad is scanned once, and then the mode returns to 0.
      • Mode 3: Continuous scan. When scanning completes, it just starts over again after a delay.
    • Bits 2-15: Number of APB cycles to wait before scanning each row (default value is 03C0h; bits 2-7 are 0 so the mode can be written directly to F50000)
    • Bits 16-31: Number of APB cycles to wait between scans (default value is 0F00h)
  • F50004 (R/W):
    • Bits 0-7: Number of rows to read (later rows are not updated in F50010-F5002F, and just read as whatever they were before being disabled)
    • Bits 8-15: Number of columns to read (later column bits in a row are set to 0 when it is updated)
  • F50008 (R/W): Keypad interrupt status/acknowledge (3-bit). Write "1" bits to acknowledge.
    • Bit 0: Keypad scan complete
    • Bit 1: Keypad data register changed
    • Bit 2: Key pressed in mode 1
  • F5000C (R/W): Keypad interrupt mask (3-bit). Set each bit to 1 if the corresponding event in [F50008] should cause an interrupt.
  • F50010-F5002F (R): Keypad data, one halfword per row.
  • F50030-F5003F (R/W): Keypad GPIOs. Each register is 20 bits, with one bit per GPIO. The role of each register is unknown.

Using the keypad

  • This is the layout of what the keypad looks like according to the controller:
Address Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7
F50012 graph trace zoom wind y= 2nd mode del
F50014 sto ln log x^2 x^-1 math alpha
F50016 0 1 4 7 , sin apps X
F50018 . 2 5 8 ( cos prgm stat
F5001A (-) 3 6 9 ) tan vars
F5001C enter + - * / ^ clear
F5001E down left right up
  • Note: Group F5001A Bit 0 is NEGATE, not to be confused with SUBTRACT.
  • Note: Group F50014 Bit 0 would be ON, but the ON key is tested elsewhere.

The controller works by scanning multiple rows into data registers; rather than manually selecting rows like previous versions.

For example, if you set the controller to scan 3 rows, it will affect only the data in F00010h, F00012h, F00014h, and leave the others alone. There's not really a reason to set anything other than 8 rows, though.

You will want to disable interrupts when performing your own scans, as OS interrupts will modify the controller's state.

Alternatively, if you want to make use of the OS's scans, you will want to first check the scan mode to ensure the data registers are valid. The OS leaves the controller in mode 1 when no keys are pressed, which renders the data registers useless.


The CE appears to use the same keypad controller as the TI-Nspire series.


Scanning the Keypad

 di             ; Disable OS interrupts
 ld hl,0F50000h
 ld (hl),2      ; Set Single Scan mode

 xor a,a
 cp a,(hl)      ; Wait for Idle mode
 jr nz,scan_wait

 ; Read data registers here as needed

 ei             ; Enable OS interrupts

It is generally a good idea to reset the keypad controller back before exiting your program, in case you have modified timings and such.

Reset the Keypad

 ld hl,0F50000h
 xor a		; Mode 0
 ld (hl),a
 inc l		; 0F50001h
 ld (hl),15	; Wait 15*256 APB cycles before scanning each row
 inc l		; 0F50002h
 xor a
 ld (hl),a
 inc l		; 0F50003h
 ld (hl),15	; Wait 15 APB cycles before each scan
 inc l		; 0F50004h
 ld a,8		; Number of rows to scan
 ld (hl),a
 inc l		; 0F50005h
 ld (hl),a	; Number of columns to scan