Routines
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62D0: Move the characters
Used by the routine at F6B4.
Input
Output
62D0 CALL \$62D6 Move one character
62D3 CALL \$62D6 Move the next character
62D6 LD HL,\$7FFC
62D9 LD A,(HL) A=number of the character last moved (0xB7-0xD1, 0xD3-0xD6)
62DA INC A A=number of the next character to move
62DB CP \$D2 Is it ERIC?
62DD JR Z,\$62DA Jump if so (we don't want to move ERIC!)
62DF CP \$D7 Have we completed an entire cast movement cycle?
62E1 JR C,\$62E5 Jump if not
62E3 LD A,\$B7 Back to 0xB7 (little girl no. 1) if so
62E5 CP \$C6 Are we dealing with little girls 1-7 or little boys 1-8?
62E7 JR NC,\$6310 Jump if not
It's the turn of one of the little girls (0xB7-0xBD), or one of the first 8 little boys (0xBE-0xC5). But if the part of the play area currently on-screen is somewhere this character never ventures into, we skip ahead to the next suitable candidate. Specifically, the following characters are skipped depending on the value of X (the leftmost column of the skool on-screen):
X Skip
X<=72 girls 1-7 (0xB7-0xBD)
80<=X<=112 girls 4-7 and boys 1-3 (0xBB-0xC0)
X>=120 boys 1-8 (0xBE-0xC5)
62E9 LD E,A E=character number (0xB7-0xC5)
62EA LD D,\$BE 0xBE=little boy no. 1
62EC LD A,(\$7FFF) A=leftmost column of the play area on screen
62EF CP \$50 This is the x-coordinate of the middle of the assembly hall stage
62F1 JR NC,\$62FA Jump if we can't see to the left of this
We are deep into the boys' skool, where no girls ever set foot.
62F3 LD A,E A=character number (0xB7-0xC5)
62F4 CP D Is this a little boy?
62F5 JR NC,\$6310 Move him if so
62F7 LD A,D Otherwise bypass the little girls and skip ahead to little boy no. 1 (0xBE)
62F8 JR \$6310
The leftmost column of the play area on screen is at least 80.
62FA CP \$78 This x-coordinate is about halfway between the tree and the gate
62FC LD A,E A=character number (0xB7-0xC5)
62FD JR C,\$6306 Jump if we can't see the first half of the girls' playground
The leftmost column of the play area on screen is at least 120. Little boys 1-8 never set foot here.
62FF CP D Is this a little girl?
6300 JR C,\$6310 Move her if so
6302 LD A,\$C6 Otherwise bypass little boys 1-8 and skip ahead to little boy no. 9 (0xC6)
6304 JR \$6310
The leftmost column of the play area on screen is between 80 and 112. Little girls 4-7 and little boys 1-3 never visit these parts.
6306 CP \$BA Is this little girl no. 1-3?
6308 JR C,\$6310 Move her if so
630A CP \$C1 Is this little boy no. 4-8?
630C JR NC,\$6310 Move him if so
630E LD A,\$C1 Otherwise bypass little girls 4-7 and little boys 1-3 and skip ahead to little boy no. 4 (0xC1)
We've now determined which character to move next. His character number is in A.
6310 LD (HL),A Store the number of the character to be moved next in 7FFC
6311 LD H,A Point HL at byte 0x1E of this character's buffer
6312 LD L,\$1E
6314 DEC (HL) Is it time to consider a change in walking speed?
6315 JR NZ,\$6339 Jump if not
It's time to consider a change in walking speed. If the character is a boy or girl, decide whether they will walk or run for the next little while.
6317 CALL \$6291 A=random number
631A AND \$1F 0x00<=A<=0x1F
631E RRA 0x10<=A<=0x1F (and the carry flag is set if the random number was odd)
631F LD (HL),A Place this number into byte 0x1E of the character's buffer
6320 SBC A,A A=0x00 if the random number was even, 0xFF otherwise
6321 DEC L L=0x1D
6322 AND \$80 A=0x00 (character will walk) or 0x80 (character will run if he's a kid)
6324 OR (HL) Superimpose the current contents of byte 0x1D
6325 BIT 6,(HL) Is this a human character (0xB7<=H<=0xD1)?
6327 JR NZ,\$632D Jump if not
We're dealing with a human character. Bit 4 of byte 0x1D of the character's buffer is never set, but if it were, it would make the character run until the current command list routine has finished. Check bit 4 of byte 0x1D now.
6329 BIT 4,(HL) Bit 4 of byte 0x1D is unused and always reset
632B JR Z,\$6331 Always make this jump
632D OR \$80 Ensure that bit 7 of byte 0x1D is set for non-human characters
632F JR \$6337
6331 BIT 5,(HL) Is this an adult character (0xC8<=H<=0xCD)?
6333 JR Z,\$6337 Jump if not
6335 AND \$7F Ensure that bit 7 of byte 0x1D is reset for adult characters (to make them walk)
6337 LD (HL),A Restore byte 0x1D with bit 7 set (run) or reset (walk) as appropriate
6338 INC L L=0x1E
Now to determine whether to move the character this time round. The answer will be yes if byte 0x1E (which is decremented on each pass through this routine) is even, or bit 7 of byte 0x1D is set (indicating that the character is either running or non-human).
6339 BIT 0,(HL) Is the counter at byte 0x1E currently even?
633B JR Z,\$6341 Jump if so (half the time)
633D DEC L L=0x1D
633E BIT 7,(HL) Is the character both human and not running?
6340 RET Z Return if so
The character shall be moved. From this point, the following steps are taken:
Step Action
1 If there is an uninterruptible subcommand routine address in bytes 0x11 and 0x12 of the character's buffer, jump to it
2 If there is a continual subcommand routine address in bytes 0x17 and 0x18 of the character's buffer, call it (and then return to step 3)
3 If there is an interruptible subcommand routine address in bytes 0x09 and 0x0A of the character's buffer, jump to it
4 Restart the command list if bit 0 of byte 0x1D of the character's buffer is set (and carry on to step 5)
5 If there is a primary command routine address in bytes 0x03 and 0x04 of the character's buffer, jump to it
6 Remove any continual subcommand routine address from bytes 0x17 and 0x18 of the character's buffer
7 Collect the next primary command routine address from the command list, place it into bytes 0x03 and 0x04 of the character's buffer, and jump to it
The address of one of the following uninterruptible subcommand routines (or an entry point thereof) may be present in bytes 0x11 and 0x12 of the character's buffer:
5F08 Make HAYLEY hit ERIC
6670 Deal with a character who's been dethroned (1)
667F Deal with a character who's been dethroned (2)
6697 Deal with a character who is looking for a seat
6D25 Make a boy sit still until assembly is finished
70B7 Make a character open or close a door
720A Control the bike when ERIC's not sitting on the saddle
74C8 Control the descent of the water, sherry or conker
7596 Deal with a character who has been knocked over
76AC Control the flight of a catapult pellet
77B3 Deal with BOY WANDER when he is firing
7813 Deal with ANGELFACE when he is hitting
7854 Deal with the frog when it has been knocked out of a cup
78BA Control the frog
7966 Control a female character while she's standing on a chair or jumping (1)
7974 Make a female character stand on a chair or start jumping
7A16 Control a mouse
D224 Make a character do nothing
F3B2 Control an open desk lid
F88B Control a stinkbomb cloud
F8F5 Make MR WACKER find a window to open after smelling a stinkbomb
F9D8 Control water fired from the pistol
FAAF Control a watered plant
The address of one of the following continual subcommand routines (or an entry point thereof) may be present in bytes 0x17 and 0x18 of the character's buffer:
775B Make BOY WANDER fire his catapult now and then
F4CC Make ALBERT keep an eye out for ERIC during lessons
F7DF Make ANGELFACE stalk HAYLEY
F804 Make ANGELFACE or BOY WANDER hit or fire now and then
The address of one of the following interruptible subcommand routines (or an entry point thereof) may be present in bytes 0x09 and 0x0A of the character's buffer:
63ED Guide a character to an intermediate destination
6438 Guide a character up a staircase
644D Guide a character down a staircase
680F Make a teacher wipe a blackboard
6880 Make a character write on a blackboard
6A08 Make a character speak
7E7B Make MISS TAKE chase ERIC (2)
F017 Make EINSTEIN speak
F09B Make a teacher find the truant ERIC
F54A Make MR WACKER find the truant ERIC
6341 LD L,\$12 Jump if there is an uninterruptible subcommand routine address in bytes 0x11 and 0x12 of the character's buffer
6343 LD A,(HL)
6344 AND A
6345 JR NZ,\$6387
6347 LD L,\$18 Jump if there is no continual subcommand routine address in bytes 0x17 and 0x18 of the character's buffer
6349 LD A,(HL)
634A AND A
634B JR Z,\$6358
634D PUSH HL Save the character number
634E LD BC,\$6357 Push 6357 (the address of the entry point to return to) onto the stack
6351 PUSH BC
6352 LD B,A Collect the address of the continual subcommand routine from bytes 0x17 and 0x18 of the character's buffer into BC and push it onto the stack
6353 DEC L
6354 LD C,(HL)
6355 PUSH BC
6357 POP HL Restore the character number to H
This entry point is used by the routine at 6394.
6358 LD L,\$0A Jump if there is an interruptible subcommand routine address in bytes 0x09 and 0x0A of the character's buffer
635A LD A,(HL)
635B AND A
635C JR NZ,\$6387
If we get here, that means there's no uninterruptible subcommand routine address in bytes 0x11 and 0x12 and no interruptible subcommand routine address in bytes 0x09 and 0x0A of the character's buffer at the moment. We take this opportunity to check whether a command list restart has been requested, by inspecting bit 0 of byte 0x1D. This bit is set in the following routines on particular occasions:
Routine Occasion
7D3E MISS TAKE needs to chase ERIC out of the girls' skool
F09B A teacher must find the absent ERIC during class, dinner or assembly
F4CC MR WACKER must find the truant ERIC
F532 MR WACKER must find and expel ERIC
F74D Lesson has ended
In addition, a command in the command list may have requested a restart (see F073, F0B8, F46C and F80D).
635E LD L,\$1D Check bit 0 of byte 0x1D: do we need to restart the command list?
6360 BIT 0,(HL)
6362 JR Z,\$6371 Jump if not
6364 RES 0,(HL) Reset bit 0 of byte 0x1D now that we are going to restart
6366 LD D,H D=character number
6367 LD L,\$1B Point HL at where the address of the character's current command list is held
6369 LD E,\$19 Point DE at where the address of the place reached in the character's current command list is held
636B LDI Copy the former into the latter (thus returning to the start of the command list)
636D LDI
636F JR \$637B
6371 LD L,\$04 Jump if there is a primary command routine address in bytes 0x03 and 0x04 of the character's buffer
6373 LD A,(HL)
6374 AND A
6375 JR NZ,\$6387
There is no primary command routine address in bytes 0x03 and 0x04 of the character's buffer, which means it's time to move to the next command in the list.
6377 LD L,\$1D Reset bit 3 of byte 0x1D, indicating that this character may not be considered for teleportation for the remainder of this lesson (see 61C2)
6379 RES 3,(HL)
637B RES 4,(HL) Reset bit 4 of byte 0x1D, indicating that the character should no longer run if he was doing so (though this bit is unused and always reset)
637D LD L,\$18 Remove the address of any continual subcommand routine from bytes 0x17 and 0x18 of the character's buffer
637F LD (HL),\$00
This entry point is used by the routine at F7D7.
6381 LD L,\$03 Collect the routine address of the next command in the character's current command list and place it into bytes 0x03 and 0x04 of the buffer
6383 CALL \$6264
6386 INC L L=0x04
6387 LD B,(HL) Collect the command routine address from bytes 0x03 and 0x04, bytes 0x09 and 0x0A, or bytes 0x11 and 0x12 of the character's buffer into BC
6388 DEC L
6389 LD C,(HL)