Spectrum ROM | Routines |
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The address of this routine is found in the table of addresses. It is called indirectly via fp_calc_2.
This subroutine handles the function USR X$, where X$ is a string. The subroutine returns in BC the address of the bit pattern for the user-defined graphic corresponding to X$. It reports error A if X$ is not a single letter between 'a' and 'u' or a user-defined graphic.
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usr | 13500 | CALL STK_FETCH | Fetch the parameters of the string X$. | ||||
13503 | DEC BC | Decrease the length by 1 to test it. | |||||
13504 | LD A,B | If the length was not 1, then jump to give error report A. | |||||
13505 | OR C | ||||||
13506 | JR NZ,REPORT_A | ||||||
13508 | LD A,(DE) | Fetch the single code of the string. | |||||
13509 | CALL ALPHA | Does it denote a letter? | |||||
13512 | JR C,USR_RANGE | If so, jump to gets its address. | |||||
13514 | SUB 144 | Reduce range for actual user-defined graphics to 0-20 decimal. | |||||
13516 | JR C,REPORT_A | Give report A if out of range. | |||||
13518 | CP 21 | Test the range again. | |||||
13520 | JR NC,REPORT_A | Give report A if out of range. | |||||
13522 | INC A | Make range of user-defined graphics 1 to 21 decimal, as for 'a' to 'u'. | |||||
USR_RANGE | 13523 | DEC A | Now make the range 0 to 20 decimal in each case. | ||||
13524 | ADD A,A | Multiply by 8 to get an offset for the address. | |||||
13525 | ADD A,A | ||||||
13526 | ADD A,A | ||||||
13527 | CP 168 | Test the range of the offset. | |||||
13529 | JR NC,REPORT_A | Give report A if out of range. | |||||
13531 | LD BC,(23675) | Fetch the address of the first user-defined graphic (UDG) in BC. | |||||
13535 | ADD A,C | Add C to the offset. | |||||
13536 | LD C,A | Store the result back in C. | |||||
13537 | JR NC,USR_STACK | Jump if there is no carry. | |||||
13539 | INC B | Increment B to complete the address. | |||||
USR_STACK | 13540 | JP STACK_BC | Jump to stack the address. | ||||
Report A - Invalid argument.
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REPORT_A | 13543 | RST 8 | Call the error handling routine. | ||||
13544 | DEFB 9 |
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