NorthStar HORIZON Manual page 52

2BR 3B pin 5 "Twice Bit Rate", low at first,
4us square wave for 32us when RE
goes high, then 2us square wave
DDI
4B pin 9
HE
14C pin 5
OP-AMP-OUTPUT Right side R7
DATA WINDOW 4D pin 5
WIND DATA 4D pin 9
"Double-Density Indicator",
goes HIGH at 512us (32us after RE)
"Hunt Enable", goes HIGH at 736us
See Note 1.
May begin either HIGH or LOW,
then 4us square waves after RE
"Separated Data", always LOW
except for 8 extremely narrow
pulses at ACQUIRE
RSn
BODY
15D pins 3,4,5,
6',10,11,12,13
5B pin 10
"Read Shift Register",
outputs always LOW
LOW
all
Note 1: Initializes during WINDOW by slewing to +5 volts.
During ACQUIRE there will be numerous small positive or
negative pulses (phase corrections). A DC shift of less
than 1/4 volt may be seen at this time if a frequency
adjustment occurs. The resultant DC level should remain
until the next WINDOW pulse.
Note 2: The two op-amp (LF356) inputs are very high
impedance and attempts to observe them with a scope probe
can affect the circuit.
A. Remove the 74LS74 IC at location 4D, lift pin 9 of the IC,
and re-insert the IC so that pin 9 is not inserted in the IC
socket. Then, with the computer reset switch depressed,
check of the following signals:
SIGNAL
BODY
SYNC BLANK
LOCATION
5B pin 10
IB pin 13
DESCRIPTION
Goes HIGH at 780us
pulse beginning at 780us,
duration 38-50us
B. Re-insert the pins of the IC's at locations 14C and 4D into
their IC sockets and remove the clip lead or soldered wire.
The disk controller board is now checked-out. If the disk
controller is to be used in applications where a special drive
motor off time is required, then refer to the Disk Controller
Configuration Options section for details. Also, if the disk
North Star HORIZON Computer
52