Table of Contents
Advertisement
3.4
OUTPUT CONTROL LINES
A. INDEX/SECTOR
Functional Description
The Index signal is provided once eash revolution (166.667 milliseconds nominal) to indicate the
beginning of a track to the controller. The Index line remains in a low (true) state forthe duration of the
index pulse. The duration of the Index pulse is nominally 2.0 milliseconds. Two index sensors are
supplied for use with single- or double-sided media.
The leading edge of an Index pulse is always used for timing to ensure diskette interchangeability
between drives.
With a standard, soft-sectored diskette installed, the signal at R33 (see Figures 3-7 and 3-8) is a high
going pulse, nominally 2.0 milliseconds in duration, every 166.667 milliseconds.
Circuit Description
Light from the Index L.
E.
D. is used to drive the index sensor, which is applied to the inverting input of
U32. This signal is conditioned by U32, then inverted by U33. It is used to drive U26. Then the
Respective index pulses are gated by U20, then with drive select by U4 to generate the signal index.
U26 and the associated support integrated circuits U16 and U20 are configured to allow only the
Index 1 signal to be present on the interface when a two-hole diskette envelope is used.
When a double-sided diskette is installed, the signal IN 1FF+ is generated and gated by U4 to enable
the output TWO SIDED.
B. Ready
Functional Description
Ready is used by the controller to ascertain the status of the drive. This signal is generated when the
drive motor is on, the diskette installed, and the drive is selected. The signal takes less than 700
milliseconds to go true (low) from a motor start by Drive Select or Head Load (see Section 1.19.21).
Circuit Description
The index pulse is gated by U5, which in turn, triggers U17, a 220 millisecond retriggerable one shot.
When the index-to-index time becomes less than 220 milliseconds, the one shot becomes
continuously enabled and generates the signal SPIN-.
This signal is gated with POR+, Power On Reset, to enable the two-revolution counters U18. The
output of U18, Pin 8, enables U6, whose output is gated with Drive Select to generate the signal
ready. Whenever the drive motor is disabled, MTRON+ goes low, causing this sequence to be
repeated when the motor is restarted.
C. Disk Change
Functional Description
The signal DISK CHANGE is used to indicate the host controller that a disk change operation has
been made.
3-10
Advertisement
Table of Contents
