Difference between revisions of "OSBYTE &A1"
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[[Category:OSBYTE]] | [[Category:OSBYTE]] | ||
| − | ==Read configuration | + | ==Read non-volatile configuration memory== |
On entry: | On entry: | ||
| − | X=byte to read or 255 | + | X=offset to byte to read or 255 to read memory size |
On exit: | On exit: | ||
| − | X | + | If unsupported: X=&FF |
| − | Y=byte read or | + | Y=preserved |
| + | If offset within non-volative memory exists: | ||
| + | X=absolute offset within memory | ||
| + | Y=byte read | ||
| + | If offset within non-volatile memory does not exist (past last location): | ||
| + | X=preserved | ||
| + | Y=preserved | ||
| + | If reading size of non-volatile memory: | ||
| + | X=&FF (ie, preserved) | ||
| + | Y=maximum offset (ie size-1), or zero if call supported and | ||
| + | no memory present, or preserved if call unsupported | ||
| − | OSBYTE &A1 reads a byte from | + | OSBYTE &A1 reads a byte from non-volatile memory used to store configuration data. |
| − | 50 locations but implementations can have more. The Master 128 uses 50 bytes | + | There are typically 50 locations but implementations can have more. The Master 128 |
| − | of nonvolatile CMOS RAM, the Master Compact uses a 128-byte or a 256-byte EEPROM, | + | uses 50 bytes of nonvolatile CMOS RAM, the Master Compact uses a 128-byte or a |
| − | the Master Extension ROM for the BBC B uses a block of memory or a file on disk. | + | 256-byte EEPROM, the Master Extension ROM for the BBC B uses a block of memory or |
| + | a file on disk. | ||
| + | |||
| + | The presence and size of the non-volatile memory can be read with the following code: | ||
| + | |||
| + | A%=161:X%=0:U%=USR&FFF4 | ||
| + | X%=(U%AND&FF00)DIV256 | ||
| + | This will set X% to <>&FF if non-volatile memory access via OSBYTE &A1 exists, or &FF if absent. | ||
| − | |||
A%=161:X%=255:Y%=49:U%=USR&FFF4 | A%=161:X%=255:Y%=49:U%=USR&FFF4 | ||
| − | |||
Y%=(U%AND&FF0000)DIV65536 | Y%=(U%AND&FF0000)DIV65536 | ||
| − | This | + | This will set Y% to the memory size minus 1, typically 49, 127 or 255, or 0 for not present. |
The following code will read all the configuration data. | The following code will read all the configuration data. | ||
Revision as of 22:45, 26 August 2024
Read non-volatile configuration memory
On entry:
X=offset to byte to read or 255 to read memory size
On exit:
If unsupported: X=&FF
Y=preserved
If offset within non-volative memory exists:
X=absolute offset within memory
Y=byte read
If offset within non-volatile memory does not exist (past last location):
X=preserved
Y=preserved
If reading size of non-volatile memory:
X=&FF (ie, preserved)
Y=maximum offset (ie size-1), or zero if call supported and
no memory present, or preserved if call unsupported
OSBYTE &A1 reads a byte from non-volatile memory used to store configuration data. There are typically 50 locations but implementations can have more. The Master 128 uses 50 bytes of nonvolatile CMOS RAM, the Master Compact uses a 128-byte or a 256-byte EEPROM, the Master Extension ROM for the BBC B uses a block of memory or a file on disk.
The presence and size of the non-volatile memory can be read with the following code:
A%=161:X%=0:U%=USR&FFF4 X%=(U%AND&FF00)DIV256
This will set X% to <>&FF if non-volatile memory access via OSBYTE &A1 exists, or &FF if absent.
A%=161:X%=255:Y%=49:U%=USR&FFF4 Y%=(U%AND&FF0000)DIV65536
This will set Y% to the memory size minus 1, typically 49, 127 or 255, or 0 for not present.
The following code will read all the configuration data.
A%=161:X%=255:Y%=49 max%=((USR&FFF4)AND&FF0000)DIV65536 DIM mem% max% FOR X%=0 TO max% mem%?X%=((USR&FFF4)AND&FF0000)DIV256 NEXT X%
See Also
- Write configuration data OSBYTE &A2
- CMOS configuration RAM allocation
- mdfs.net OSBYTE list
Jgharston 22:15, 26 May 2009 (UTC)
