====== NEC PC-9801 - INT 18h ======

===== AH = 00h - Get Keystroke =====

**Input:**

  * AH = 00h

**Output:**

  * AX = keystroke

The keystroke is removed from the input buffer.

TODO: Blocks until a keystroke is received?

===== AH = 01h - Check Keystroke =====

**Input:**

  * AH = 01h

**Output:**

  * AX = keystroke
  * BH = 1 if keystroke in buffer, else 0.

The keystroke is NOT removed from the input buffer.

===== AH = 02h - Get Shift Status =====

**Input:**

  * AH = 02h

**Output:**

  * AL = shift flags:
    * bit 0 - SHIFT (pressed)
    * bit 1 - CAPS (held)
    * bit 2 - KANA (held)
    * bit 3 - GRPH (pressed)
    * bit 4 - CTRL (pressed)

===== AH = 03h - Initialize Keyboard Interface =====

TODO


===== AH = 04h - Access Keystroke Bitmap =====

**Input:**

  * AH = 04h
  * AL = byte of keystroke bitmap (bits 0-3)

**Output**

  * AH = keystroke bitmap value (byte at ''52Ah + (AL & 0x0F)'')

TODO

===== AH = 05h - Get and Check Keystroke =====

**Input:**

  * AH = 00h

**Output:**

  * AX = keystroke
  * BH = 1 if keystroke in buffer, 0 otherwise.

The keystroke is removed from the input buffer.

Non-blocking. Seems to be a combination of AH = 01h and AH = 00h.

===== AH = 0Ah - Set GDC Display Mode ====

TODO

===== AH = 0Bh - Get GDC Display Mode ====

TODO

===== AH = 0Ch - Enable GDC Text Layer ====

TODO

===== AH = 0Dh - Disable GDC Text Layer ====

TODO

===== AH = 0Eh - Set GDC Text Display Area ====

**Input:**

  * AH = 0Eh
  * DX = offset

TODO

===== AH = 11h - Show Cursor ====

**Input:**

  * AH = 11h

===== AH = 12h - Hide Cursor ====

**Input:**

  * AH = 12h

===== AH = 13h - Set Cursor Position ====

**Input:**

  * AH = 13h
  * DX = offset

TODO

===== AH = 14h - Read Custom Glyph =====

Input:

  * AH = 14h
  * BX:CX = glyph data destination (34 bytes, 16x16)
  * DX = glyph code

TODO

===== AH = 16h - Fill Text Display =====

**Input:**

  * AH = 16h
  * DH = attribute
  * DL = character

===== AH = 17h =====

TODO

===== AH = 18h =====

TODO

===== AH = 1Ah - Write Custom Glyph =====

Input:

  * AH = 1Ah
  * BX:CX = glyph data (34 bytes, 16x16)
  * DX = glyph code (must be 0x76xx or 0x77xx, count of custom glyphs limited)

TODO

===== AH = 31h =====

TODO

===== AH = 40h - Enable Graphics Layer =====

Input:

  * AH = 40h

TODO

===== AH = 41h - Disable Graphics Layer =====

Input:

  * AH = 41h

TODO

===== AH = 42h - Configure Graphics Mode =====

TODO

===== AH = 43h =====

TODO

===== AH = 4Dh =====

TODO