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49 lines
1.8 KiB
Z80 Assembly
49 lines
1.8 KiB
Z80 Assembly
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;+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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; C L R H I S T
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; for ZPM3
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; by Simeon Cran
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; 26/4/92
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;
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; This program clears the ZPM3 function 10 history buffer. It is presented in
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; source code form to inform users about how the facility is manipulated.
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; The only real use for clearing the history buffer is as a security feature
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; on RZPM3 systems (remote ZPM3 systems (such as BBSes)). Note that individual
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; commands may be cleared from the history buffer with control-V.
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;+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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; SYNTAX:
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; CLRHIST Clears the history buffer
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;+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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;
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; The history buffer is cleared by setting bit 7 of offset 85h of the SCB page.
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; This offset can not be directly accessed by the SCB function (31h). Instead
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; we get the SCB base page with function 31h, and then find the offset from
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; there. No other bits in the byte may be touched.
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;===============================================================================
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BDOS equ 5
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deffcb equ 5ch
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SCBfunc equ 31h ; Get/Set SCB function number
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SCBoff equ 3bh ; Offset in SCB to get SCB base page
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CLHoff equ 85h ; Offset in SCB base page of Clear History buffer bit.
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jp start ; Jump over general data
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start: ; Get the address of the bit which controls History buffer clearing
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ld c,SCBfunc
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ld de,SCBPB
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call bdos ; Get base page of SCB
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ld h,a
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ld l,CLHoff ; HL is now the address of the byte
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set 7,(hl) ; All to do
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rst 0
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SCBPB: ; System control block function parameter block.
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db 03bh
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db 0 ; Get operation
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