24h FL$BOPN open a block file
Input X = addresse of block file name (leading count byte).
B = block file type
Output D = length of data in block file

Finds a named block file of the given block file type data.

On return D is the length of the data, and the pack address is set to the start of the data, ready for PK$READ to load the data into RAM. The file name is a leading byte count string at X in the form <pack>:<name>.

Error file not found will be reported if the file does not exist.

        LDAB    #84h            ; block file type for RS232 saved setup
        LDX     #NAME           ; address of filename
        OS      FL$BOPN         ; open the file
        BCS     ERROR

        LDX     #LOAD_ADDRESS
        OS      PK$READ

Errors 194 - battery too low
200 - read pack err
234 - file not found
236 - bad file name
238 - end of file
240 - unknown pack
241 - pack not blank
243 - bad device name
245 - write pack err
246 - no pack