RK06/RK07 Disk Drive User's Manual - Trailing-Edge

3. The drive is seized by the other port. At this time, an initialize will:
a. Clear the port's attention bit
b. Cancel the port request if one is pending.
9.8 GETTING DRIVE STATUS IN DUAL-ACCESS MODE
If the drive is seized by one of the ports, that port's controller may interrogate any of the eight status
multiplexers (AO, BO, AI, Bl, A2, B2, A3, B3) within the drive.
If the drive cannot be seized (busy with another port), only status multiplexers AO and BO may be read
through the unseized port. This situation causes the Combined Error bit (bit 15 in RKCS) to be
asserted in the controller of the un seized port. Refer to Figure 9-3 for the data bits contained in drive
status messages AO through B3.
9.8.1 Status Bits Pertinent to the Dual-Port Available at the Unibus Interface
1. Drive available (DRA) - This bit is set to the port that has access to the drive and reset to the
other port. Read only.
2. Volume Valid (VV) - This bit is used to indicate when a disk cartridge may have been
changed. There is a Volume Valid bit for each port.
3. Ready (RD) - Indicates that the selected drive is up to speed and its heads are settled over the
specified cylinder. This bit will always be reset to a port not having access to the drive.
9-6