WRITE DATA (Circuit Card 1A2A6)

TM 11-6625-3024-14/EE641-AC-MMA-010/E154 SYSEX/TO 33AA50-5-1-1

The SHIFTED ONES mode is normally used to

4-5. WRITE DATA (Circuit Card 1A2A6) (See

check the transport for measurement of combined

Figure FO-5)

skew and jitter.

The Write Data circuits receive the data block

The WRITE DATA (WDO-WD7) from the data

from the write data control circuits, adds the CRC

word selector is routed through output buffers to

word, and generates parity before issuing the write

the transport. The output buffers invert the data for

data to the transport. (See Figure 4-3, Write Data

negative logic input to the transport.

Block Diagram.)

The DATA BLOCK (WCO-WC7) from write data

Each data track is applied to a parity decoder to

control circuit card is applied to the data word

check for even parity of each data byte. The output

selector. The CRC WORD pulse from the format

of the parity decoder is issued to the write data

generator circuit enables the data word selector to

control circuits.

select the input from the CRC word switches. The

switches are pre-set to the determined CRC word.

Errors are inserted by enabling the front panel

The CRC word is written during one clock period.

switch, INSERT ERRORS. This is a momentary

switch that sets an error latch, which changes the

The SHIFTED ONES IND input is issued from

parity decoder to read odd parity. Since parity

the data control circuits and selects an input to the

should always be even, odd parity from the parity

data word selector from the shifted ones selector.

decoder is detected as an error. The next clock

WCNT-1 through WCNT-4 is a binary input to the

pulse resets the error latch.

shifted ones selector. The binary input will select

one output from the selector. Each time the binary

input changes, the selected output changes. Each

selected output produces a logic one to the data

word selector. This results in a shifted ones pattern

in the WRITE DATA, as shown below.

000001000

111111111

000000100

111111111

000000010

111111111

000000001

4-6