Contact Sam Cruise: Routine at F17F

F17F: Get a random number

Used by the routines at 61CF, 621E, 62DB, 634C, 6670, 6FC8, 72B1, 77A3, 7996, 7B6A, F485, F6E9, F748, F82A, FA05 and FB52. Returns with a random number in A.
F17F	PUSH HL
F180	LD HL,($7FDE)	Collect the random number seed from 7FDE
F183	INC HL	Add 257 to it
F184	INC H	Add 257 to it
F185	LD ($7FDE),HL	Store the new seed
F188	LD A,($5C78)	Collect the LSB of the system variable FRAMES, which is incremented every 20ms
F18B	XOR (HL)	A=random number
F18C	POP HL
F18D	RET