HOW TO PLAY

A "scripted" how-to-play screen.

The HOW_TO_PLAY ($C00474) system ROM call builds and animates an "how to play" screen from a command list. Only a few games use this call.

The graphics are set up using the fix layer with hardcoded tile numbers.

Command list

The command list must be loaded at $10F300 (how many bytes reserved ?).

Each command is a longword (4 bytes):

• The rightmost byte is the command parameter
• The next byte is the command type (0~3)
• If the command type isn't recognized, the longword is processed as being a pointer to a MESS OUT data buffer
• The end command is $00000000

00000000 00000000 000000TT PPPPPPPP

Type 0: Loop control

• If the parameter byte is less than $FF: Set a loop counter to that value
• If the parameter byte is equal to $FF: Decrement the loop counter and loop back to the previous setup command until it reaches 0

Type 1: Joystick state

Sets the color of each joystick direction arrow.

• 1 is light blue (pressed)
• 0 is dark blue (released)

Bit	7	6	5	4	3	2	1	0
Def	Up-Right	Right	Down-Right	Down	Down-Left	Left	Up-Left	Up

If followed by a null command ($0.l) the next 16-bit word specifies a number of frames to wait before executing the next command.

Type 2: Buttons state

Sets the state of each button.

• 1 is pressed
• 0 is released

Bit	7	6	5	4	3	2	1	0
Def	-				D	C	B	A

If followed by a null command ($0.l) the next 16-bit word specifies a number of frames to wait before executing the next command.

Any other type: Text update

The longword value is a pointer to a MESS_OUT data buffer.

This command is always followed by a 16-bit word value which specifies a number of frames to wait before executing the next command.

Example

NAM-1975 sets up the following command list:

0000 0200    All buttons released
0000 01FF    All arrows highlighted
0010 F3E2    MESS_OUT write "NAM 1975" "CONTROL HERO AND CURSOR"
0004         Wait 4 frames
0000 000C    Init loop counter to 12
0000 0100    All arrows cleared       <--------------,
0000 0000    Wait...                                 |
0008         ...8 frames                             |
0000 01FF    All arrows highlighted                  |
0000 0000    Wait...                                 |
0008         ...8 frames                             |
0000 00FF    Loop back (blink all arrows 12 times) --'
0000 0201    A button is pressed
0000 0100    All arrows cleared
0010 F418    MESS_OUT write "MACHINE GUN"
0004         Wait 4 frames
0000 000C    Init loop counter to 12
0000 0200    All buttons released     <--------------,
0000 0000    Wait...                                 |
0008         ...8 frames                             |
0000 0201    A button is pressed                     |
0000 0000    Wait...                                 |
0008         ...8 frames                             |
0000 00FF    Loop back (blink A button 12 times) ----'
...

List of games known to use HOW_TO_PLAY

• NAM-1975
• Baseball Stars Professional
• Mahjong Kyo Retsuden
• ...

Tilemap

how-to-play tilemap, with each 8x16 block turned into the low-byte of it's hex address

The tiles that make up the HOW_TO_PLAY screen are found in pages 7 and 8 of the Fix rom. Much like how MESS OUT handles 8x16 text, each tile in page 7 has a counterpart at the same position on page 8, which gets displayed immediately below. (The exception to this is the black tiles around the edges, which are all 0x07FF.)
Given this unifom layout of adjacent rows, the below table combines each pair and lists only the low byte.

The interior of the lower text area is initialized with rows of 0x9920 and 0x9A20; the 8x16 spaces from fontset 9, in palette 9.

Overall Layout

FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF	FF
FF	00	01	04	05	05	05	05	05	05	05	05	05	05	05	05	05	05	05	06	07	07	07	07	07	07	07	07	07	07	07	07	07	07	07	07	07	07
FF	02	03	08	09	09	09	09	09	09	09	09	09	09	09	09	09	09	09	0A	0B	0B	0B	0B	0B	0B	0B	0B	0B	0B	0B	0B	0B	0B	0B	0B	0B	0B
FF	03	03	0C	0D	0E	0F	10	11	12	13	14	15	0F	0F	0F	0F	0F	0F	0F	0F	0F	0F	0F	0F	0F	0F	0F	0F	0F	0F	0F	0F	0F	0F	63	64	65
FF	03	03	0C	5C	5D	5D	16	17	18	19	1A	1B	5D	5D	5D	5D	5D	5D	5D	5D	2C	2D	2E	2F	30	31	32	33	34	35	36	37	5D	5D	5D	5D	5D
FF	03	03	0C	5D	5D	5D	1C	1D	1E	1F	20	21	5D	5D	5D	5D	5D	38	39	3A	3B	3C	3D	3E	3F	40	41	42	43	44	45	46	5D	5D	5D	5D	5D
FF	03	03	0C	5E	5D	5D	22	23	24	25	26	27	5D	5D	5D	5D	5D	47	48	49	4A	4B	4C	4D	4E	4F	50	51	52	53	54	55	5D	5D	5D	5D	5D
FF	03	03	0C	5F	5D	5D	5D	28	29	2A	2B	5D	5D	5D	5D	5D	5D	56	57	58	59	59	59	59	59	59	59	59	59	59	5A	5B	5D	5D	5D	5D	5D
FF	68	69	0C	60	61	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	62	66	67
FF	6A	6B	6C	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	6D	76	77	77	77
FF	03	03	6F	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	78	79	79	79
FF	6E	03	70	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	7A	7B	7B	7B
FF	72	73	71	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	20	7C	7D	7D	7D
FF	FF	FF	74	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	75	7E	FF	FF	FF

• The joystick (10-2B) uses palette 0x0, which changes to highlight the directions.
  • Colors 0x5-0xC map to the joystick directions, starting at Up and rotating anticlockwise.
  • Note: the top-halves of tiles 10-15 are in palette 0xD instead.
• The buttons (2C-5B) use palette 0xA when dim, and 0xB when illuminated.
  • A tiles: 38-3B, 47-4B, 56-58
  • B tiles: 2C-2F, 3C-3E, 4C-4D
  • C tiles: 30-33, 3F-42, 4E-51
  • D tiles: 34-37, 43-46, 52-55
• The text-boxes frames (04-06, 08-0A, 6C-6D, 6F-71, 74-76, 78, 7A, 7C, 7E) have palette 0xC.
• The rest of the control panel uses palette 0xD.