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Used by the routine at PO_ABLE.
Ordinary character codes, token codes and user-defined graphic codes, and graphic codes are dealt with separately.
A Character code
B Line number
C Column number
HL Display file address or printer buffer address
PO_ANY 02852 CP 128 Jump forward with ordinary character codes.
02854 JR C,PO_CHAR
02856 CP 144 Jump forward with token codes and UDG codes.
02858 JR NC,PO_T_UDG
02860 LD B,A Move the graphic code.
02861 CALL PO_GR_1 Construct the graphic form.
02864 CALL PO_FETCH HL has been disturbed so 'fetch' again.
02867 LD DE,23698 Make DE point to the start of the graphic form, i.e. MEMBOT.
02870 JR PR_ALL Jump forward to print the graphic character.
Graphic characters are constructed in an ad hoc manner in the calculator's memory area, i.e. mem-0 and mem-1.
PO_GR_1 02872 LD HL,23698 This is MEMBOT.
02875 CALL PO_GR_2 In effect call the following subroutine twice.
PO_GR_2 02878 RR B Determine bit 0 (and later bit 2) of the graphic code.
02880 SBC A,A
02881 AND 15 The A register will hold 0 or 15 depending on the value of the bit in the code.
02883 LD C,A Save the result in C.
02884 RR B Determine bit 1 (and later bit 3) of the graphic code.
02886 SBC A,A
02887 AND 240 The A register will hold 0 or 240.
02889 OR C The two results are combined.
02890 LD C,4 The A register holds half the character form and has to be used four times. This is done for the upper half of the character form and then the lower.
PO_GR_3 02892 LD (HL),A
02893 INC HL
02894 DEC C
02895 JR NZ,PO_GR_3
02897 RET
Token codes and user-defined graphic codes are now separated.
PO_T_UDG 02898 SUB 165 Jump forward with token codes.
02900 JR NC,PO_T
02902 ADD A,21 UDG codes are now 0 to 15.
02904 PUSH BC Save the current position values on the machine stack.
02905 LD BC,(23675) Fetch the base address of the UDG area (from UDG) and jump forward.
02909 JR PO_CHAR_2
PO_T 02911 CALL PO_TOKENS Now print the token and return via PO_FETCH.
This entry point is used by the routine at PO_RIGHT.
The required character form is identified.
PO_CHAR 02917 PUSH BC The current position is saved.
02918 LD BC,(23606) The base address of the character area is fetched (CHARS).
PO_CHAR_2 02922 EX DE,HL The print address is saved.
02923 LD HL,23611 This is FLAGS.
02926 RES 0,(HL) Allow for a leading space.
02928 CP " " Jump forward if the character is not a 'space'.
02930 JR NZ,PO_CHAR_3
02932 SET 0,(HL) But 'suppress' if it is.
PO_CHAR_3 02934 LD H,0 Now pass the character code to the HL register pair.
02936 LD L,A
02937 ADD HL,HL The character code is in effect multiplied by 8.
02938 ADD HL,HL
02939 ADD HL,HL
02940 ADD HL,BC The base address of the character form is found.
02941 POP BC The current position is fetched and the base address passed to the DE register pair.
02942 EX DE,HL
The following subroutine is used to print all '8*8' bit characters. On entry the DE register pair holds the base address of the character form, the HL register the destination address and the BC register pair the current 'line and column' values.
PR_ALL 02943 LD A,C Fetch the column number.
02944 DEC A Move one column rightwards.
02945 LD A,33 Jump forward unless a new line is indicated.
02947 JR NZ,PR_ALL_1
02949 DEC B Move down one line.
02950 LD C,A Column number is 33.
02951 BIT 1,(IY+1) Jump forward if handling the screen (bit 1 of FLAGS reset).
02955 JR Z,PR_ALL_1
02957 PUSH DE Save the base address whilst the printer buffer is emptied.
02961 POP DE
02962 LD A,C Copy the new column number.
PR_ALL_1 02963 CP C Test whether a new line is being used. If it is see if the display requires to be scrolled.
02964 PUSH DE
02968 POP DE
Now consider the present state of INVERSE and OVER.
02969 PUSH BC Save the position values and the destination address on the machine stack.
02970 PUSH HL
02971 LD A,(23697) Fetch P-FLAG and read bit 0.
02974 LD B,255 Prepare the 'OVER mask' in the B register, i.e. OVER 0=0 and OVER 1=255.
02976 RRA
02977 JR C,PR_ALL_2
02979 INC B
PR_ALL_2 02980 RRA Read bit 2 of P-FLAG and prepare the 'INVERSE mask' in the C register, i.e. INVERSE 0=0 and INVERSE 1=255.
02981 RRA
02982 SBC A,A
02983 LD C,A
02984 LD A,8 Set the A register to hold the 'pixel-line' counter and clear the carry flag.
02986 AND A
02987 BIT 1,(IY+1) Jump forward if handling the screen (bit 1 of FLAGS reset).
02991 JR Z,PR_ALL_3
02993 SET 1,(IY+48) Signal 'printer buffer no longer empty' (set bit 1 of FLAGS2).
02997 SCF Set the carry flag to show that the printer is being used.
PR_ALL_3 02998 EX DE,HL Exchange the destination address with the base address before entering the loop.
The character can now be printed. Eight passes of the loop are made - one for each 'pixel-line'.
PR_ALL_4 02999 EX AF,AF' The carry flag is set when using the printer. Save this flag in F'.
03000 LD A,(DE) Fetch the existing 'pixel-line'.
03001 AND B Use the 'OVER mask' and then 'XOR' the result with the 'pixel-line' of the character form.
03002 XOR (HL)
03003 XOR C Finally consider the 'INVERSE mask'.
03004 LD (DE),A Enter the result.
03005 EX AF,AF' Fetch the printer flag and jump forward if required.
03006 JR C,PR_ALL_6
03008 INC D Update the destination address.
PR_ALL_5 03009 INC HL Update the 'pixel-line' address of the character form.
03010 DEC A Decrease the counter and loop back unless it is zero.
03011 JR NZ,PR_ALL_4
Once the character has been printed the attribute byte is to be set as required.
03013 EX DE,HL Make the H register hold a correct high-address for the character area.
03014 DEC H
03015 BIT 1,(IY+1) Set the attribute byte only if handling the screen (bit 1 of FLAGS reset).
03022 POP HL Restore the original destination address and the position values.
03023 POP BC
03024 DEC C Decrease the column number and increase the destination address before returning.
03025 INC HL
03026 RET
When the printer is being used the destination address has to be updated in increments of 32.
PR_ALL_6 03027 EX AF,AF' Save the printer flag again.
03028 LD A,32 The required increment value.
03030 ADD A,E Add the value and pass the result back to the E register.
03031 LD E,A
03032 EX AF,AF' Fetch the flag.
03033 JR PR_ALL_5 Jump back into the loop.
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