=> R0 = 221-228 (&DD - &E5) controls range of buffer codes affected
R1 = EOR value
R2 = AND value
<= R0 preserved
R1 = previous value
R2 corrupted
This call reads or sets the interpretation of input values &80-&FF, which includes codes generated by the function keys. The 128 buffer codes are divided into 8 blocks, and the block affected is chosen by R0. The value generated via R1 and R2 determines the interpretation of buffer codes:
Value Interpretation
0 discard
1 expand function key number (code MOD 16)
2 insert 0 byte followed by code
3-255 insert (code MOD 16) + value
See PRM 1, page 891
OS_Byte 221-228 key codes
Function keys generate these codes unshifted
Key Code
Print &80
F1-F9 &81-&89
Copy &8B
Left &8C
Right &8D
Down &8E
Up &8F
Page down &9E
Page up &9F
F10-F12 &CA-&CC
Insert &CD
Shift EORs the code with &10
Control EORs the code with &20
The cursor keys and copy only generate these codes if set up to act as function keys by calling OS_Byte 4 with R1=2.
&80 + Buffer value gives the character codes used by the Wimp. When reset occurs &CA (i.e. F10) is inserted into the input buffer.
Unlisted codes cannot be generated by the main keyboard, but can occur by
· Using these OS_Byte calls to set keys to generate them
· Changing the numeric keypad base with OS_Byte 238
· Inserting bytes into the keyboard buffer with OS_Byte 138 and 153.
· Receiving bytes from the serial port (see also OS_Byte 181 to control serial input interpretation)
Note that page up and down effectively behave as Up and Down with shift toggled. In fact, it is impossible to distinguish shift/control combinations of page up and down with shift/control combinations of cursor up and down, which can prove frustrating.
OS_Byte 221-228 ranges
R0 Range affected Default value Effect
221 &C0-&CF 1 function keys (Print, F1-F9, cursor keys and copy if acting as function keys)
222 &D0-&FF &80 return buffer code - 16
223 &E0-&FF &90 return buffer code - 16
224 &F0-&FF 0 discard
225 &80-&8F 1 function keys (F10-F12, Insert)
226 &90-&9F &D0 return buffer code
227 &A0-&AF &E0 return buffer code
228 &B0-&BF &F0 return buffer code
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