Routines
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031E: THE 'K-TEST' SUBROUTINE
Used by the routines at KEYBOARD and S_INKEY.
The key value is tested and a return made if 'no-key' or 'shift-only'; otherwise the 'main code' for that key is found.
Input
D Shift key pressed (+18 or +27), or +FF if no shift key pressed
E Other key pressed (+00 to +27), or +FF if no other key pressed
Output
A Main code (from the main key table)
F Carry flag reset if an invalid combination of keys is pressed
K_TEST 031E LD B,D Copy the shift byte.
031F LD D,$00 Clear the D register for later.
0321 LD A,E Move the key number.
0322 CP $27 Return now if the key was 'CAPS SHIFT' only or 'no-key'.
0324 RET NC
0325 CP $18 Jump forward unless the E key was SYMBOL SHIFT.
0327 JR NZ,K_MAIN
0329 BIT 7,B However accept SYMBOL SHIFT and another key; return with SYMBOL SHIFT only.
032B RET NZ
The 'main code' is found by indexing into the main key table.
K_MAIN 032C LD HL,$0205 The base address of the main key table.
032F ADD HL,DE Index into the table and fetch the 'main code'.
0330 LD A,(HL)
0331 SCF Signal 'valid keystroke' before returning.
0332 RET
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