PDP11 PeripheralsHbk 1972 - Trailing-Edge

15-13 Drive Select (DR SEL) Contains binary representation of the logical
drive number currently being selected.
12-5 Cylinder Address (CYL ADD) Contains binary representation of the cyl·
inder address currently being selected.
The largest valid number is 312, .
4 Surface (SUR) When active lower disk head is enabled.
3-0 Sector Address (SA) Binary representation of the disk sector to
be addressed.
This register maybe loaded only while the RKll is in the ready state.
Maintenance Register (RKMR)
This register is provided for diagnostic purposes only and does not participate in
the norma! disk operations.
5.4.4 Cross Cylinder Operation
Surface 0 is defined as the upper surface and is active when RKDA 04 is reset. If a
transfer is initiated that requires an overflow from surface 0, the control will automatically
change to sector 0 of surface 1. If a transfer is initiated that requires an
overflow from surface 1, the control will automatically move the heads to the next
contiguous cylinder, check for proper head positioning, and continue the transfer
on sector 0 and surface 0 of the new cyclinder. An attempt to overflow out of the
last sector of the last cylinder will result in an error condition.
At the end of any transfer the RKDA is automatically incremented.
5.4.5 Hardware Poll
The control is capable of having any or all of the drives performing a SEEK or
DRIVE RESET operation at anyone time. A HARDWARE POLL feature will identify
the logical drive number in bits 13, 14 and 150f the RKDS of any drive that has
completed a SEEK or DRIVE RESET operation and cause an interrupt if bit 6
RKCS is set (IDE) and the control is in the READY state (bit 7 RKCS is set) and the
control was not already attempting to cause an interrupt as a result of some other
operation. This will occur even if Bit 6 RKCS (IDE) was not set when first initiating
the SEEK or DRIVE RESET function. If two or more drives complete the function
simultaneously, the control will interrupt once for each drive and identify each
one in turn in the RKDS. Care should be taken in this situation to raise the processor
interrupt status to a level equal to or greater than that currently held by the
RKl1 or else a second interrupt will occur immediately after the first and the end
result will be that the interrupt service routine has been interrupted. This situation
will also occur if an attempt is made to initiate a SEEK to an address that
the drive is already at since one interrupt will occur as a result of the SEEK or
DRIVE RESET function having been successfully initiated and another to report
that the heads have reached their destination, which will occur immediately because
the heads are already there.
5.4.6 interrupts
Because of the format structure of the RKll-C, any interruption of a write sequence
cannot be tolerated until the end of the sector because this would result in
essentially an unformatted disk. Therefore, any outside intervention of this operation
is held off until the end of the current sector, which includes the CONTROL
RESET function and the PROCESSOR or BUS INITIALIZE signals. Therefore, all
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