69
The interface supports the
BOOT
command to load a disc boot extension. The
BOOT DQC
command copies the
HP 12992A boot loader ROM into memory, sets the S register, and begins execution. The S register is set as
follows:
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0
1
1
0
DQD select code
unchanged
0
0
0
Bits 5-3 of the existing S-register value are retained when the
BOOT
command is executed and are available to the
boot extension program.
Loader execution ends with a jump indirect through location 2055 octal. The success or failure of the transfer is not
checked.
The Data PCA state contains these registers:
Name
Size
Radix
Action
IBUF
16
8
Input buffer
OBUF
16
8
Output buffer
DBUF [0:127]
16
8
Sector buffer
BPTR
7
10
Sector buffer pointer
CMD
1
2
Command flip-flop
CTL
1
2
Control flip-flop
FLG
1
2
Flag flip-flop
FBF
1
2
Flag buffer flip-flop
XFER
1
2
Transfer in progress flag
WVAL
1
2
Write data valid flag
