Access Control - IBM 5114 Maintenance Information Manual

Bus In Bit
5 -
Diskette 1, Diskette 2
This bit is turned off when a diskette 1 is located in the
diskette drive. This bit is turned on when a diskette 2 is
located in the diskette drive. This bit must be tested
after the index pulse has been checked.
Bus In Bit 6 - CRC Error
This bit is turned on when the CRC read from the
diskette does not agree with the generated CRC.
Bus In Bit 7 - Read/Write Overrun
This bit is turned on when the system does not service
an interrupt before the next interrupt occurs. Detection
of an overrun causes the adapter to reset to access
mode.
ACCESS CONTROL
Bus Out Bit 0 - Reset New Media
This bit resets the 'new media' latch. The latch is set
when the diskette drive cover is opened.
Bus Out Bit 1 - MFM
This bit sets the adapter to the desired recording mode.
If the bit is off, the adapter is in FM mode. If the bit is
on, the adapter is in MFM mode.
Bus Out Bit 2 - Inner Track Select (filter control)
This bit sets the inner track select (filter control) latch.
The bit is turned on and the inner track select (filter
control) latch is set when the read/write head location is
equal to or greater than track 60. This bit is turned off,
and the inner track select (filter control) latch is reset
when the read/write head location is less than track 60.
Bus Out Bit
3 -
Inner Tracks
This bit sets the inner tracks latch. This bit is turned on
and the inner tracks latch is set when the read/write head
location is equal to or greater than track 42. This bit is
turned off, and the Inner tracks latch is reset when the
read/write head location is less than track 42.
Bus Out Bit 4 - Engage Head
This bit controls the loading and unloading of the
read/write
he~ds.
This bit is turned on to load the
heads. This bit is turned off to unload the heads. If two
index pulses are detected and no commands have been
issued to the adapter, the heads are unloaded.
Bus Out Bit
5 -
Head Select
This bit selects the appropriate head for the read/write
operation. This bit is turned on to select head 1. This
bit is turned off to select head O.
Bus Out Bits 6 and 7 - Access lines
These 2 bits together control the movement of the
heads from track to track.
Tracks
00 01 02 03 04
Bus out Bit 6
1 0 0 1 1
Bus out Bit 7
1 1 0
0 1
Access Line 0
1 0 0 1 1
Access Li ne 1 1 1 0
0 1
Access Line 2
0
1
1 0 0
Access Li ne 3
0 0 1 1
0
Setting in track 00, .both bits 6 and 7 are on. This
makes access lines 0 and 1 active and access lines 2
and 3 inactive. To move the read/write heads to track
01, bit 6 must be turned off. This deactivates access
line 0 and activate accesss line 2 while leaving access
line 1 active. With these two access lines active, the
stepper motor moves the read/write heads to track 01.
Adapter Commands 3-37