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inverted and gated with Write Protect and Drive Select to enable U23, U30, and 013. Transistors 013
and 012 are write current switches. 013 and 012 are on in parallel when the low Write Current
interface is high (false). This results in a write current of 10 milliamps. When the low Write Current line
goes low (true), transistor 012 turns off, and the current decreases to 7 milliamps. R52 and R51
determine the amount of write current supplied to the head. The network CR1B, CR19, CR20, RBO
and RB1 is a power-loss write disable. If a sudden voltage loss occurs, transistor 014 turns off,
disabling the write current.
E. WRT DATA
Functional Description
When the drive is selected, the write data line provides the bit-serial Write Data pulses that control the
switching of the write current in the heads. The write electronics must be conditioned for writing by
the Write Gate line.
For each high-to-Iow transition on the WRT DATA line, a flux change is produced at the head write gap.
This causes a flux change to be stored on the diskette (see Figure 3-4).
N INTERNAL WRITE BUSY
SIDE
SELECT
LOGIC
SIDE
SELECT
NWRITE DATA
NWRITE GATE
N WRITE PROTECT
UNIT SELECT
o
a
WRITE
DATA
TRIGGER
C
WRITE
CURRENT
SOURCE
ERASE
DELAY
LOGIC
IN WRITE)
WRITE
DRIVER 1
WRITE
DRIVER 2
ERASE
CURRENT
SOURCE
READ!
WRITE
COILS
ERASE
COIL
IN INTERNAL ...... READ DISABLE
~ - - - - - - - W R I T E
BUSY)
Figure 3-4
Write Data Circuit Block Diagram
When a double-frequency type encoding technique is used (in which data and clock form the combined
Write Data signal), it is recommended that the repetition of the high-to-Iow transitions, when writing
all zeros, be equal to the nominal data rate ±0.1 percent. The repetition rate of the high-to-Iow
transitions, when writing all ones, should be equal to twice the nominal data rate ±O.1 percent. The
data transfer rate for a 1F pattern is 250,000 Bits Per Second (BPS). The data transfer rate for a 2F
pattern is 500,000 BPS.
3-6
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