Commodore Plus 4 - Page 366

354 Using Peripheral Devices
209A A9 0D LDA #$0D Carriage return character.
209C 20 D2 FF JSR $FFD2 Send to screen.
209F 20 CF FF JSR $FFCF Get a character from command channel.
20A2 20 D2 FF JSR $FFD2 Send to screen.
20A5 C9 0D CMP #$0D Compare to carriage return.
20A7 D0 F6 BNE $209F If not, get another byte.
20A9 A9 0F LDA #$0F Logical file number of command channel.
20AB 20 C3 FF JSR $FFC3 CLOSE.
20AE 20 CC FF JSR $FFOC CLRCH.
20B1 00 BRK Stop processing.
The following data need to be placed in memory:
>20P8 52 4F 52 52 45 20 00 00 :PRORRE..1
>2100 53 41 56 50 52 47 00 00 :1SAVPRG..|
Using Data Files This section outlines the machine-language equivalents for
the BASIC statements OPEN, CLOSE, GET#, and PRINT#. They can be used
for all the purposes outlined in the preceding BASIC sections, including data-file
handling and direct-access programming. The key subroutines are OPEN
(SFFCD), CLOSE (SFFC3), CHKIN (SFFC6), CHOUT (SFFC9), CLRCH
(SFFCC), BASIN (SFFCF), and BSOUT (SFFD2). Any messages printed to the
screen during these operations are controlled by the message flag set with
SETMSG ($FF90).
Open
When a file is to be opened, and a file name must be provided, the name (1 to 16
characters) and the type of file and mode (see the BASIC section on OPENing
data files) must be stored in CHR$ codes in ascending order somewhere in
memory. Exactly the same situation exists as in BASIC. That is, if the type and
mode are omitted, the mode is assumed to be read, and the type is the existing
type of the file. A direct-access channel can be opened by using a pound sign for
the file name. The following outlines the operations required:
1. Load .A with the logical file number to use for the file, .X with the device
number of the disk drive, and .Y with the channel number. Call SETLFS
($FFBA).
2. Load .A with the length of the file name (0 if no name), .X with the low byte of
the address where the file name is stored, and .Y with the high byte of the
address where the file name is stored. Call SETNAM ($FFBD).
3. Call OPEN ($FFC0).
4. Check for errors by examining the carry bit and the disk error channel. The
status byte is not particularly useful for discovering OPEN errors.