CT1820 datasheet(7/10 Pages) AEROFLEX

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SCDCT1820 REV D 6/25/99 Plainview NY (516) 694-6700

RECEIVE CYCLE OPERATION

DECODER SHIFT CLOCK (DSC) (see Figure 5)

operates at the data rate (1MHz). When the

DECODER recognises a valid sync and two valid

Manchester data bits

x, a receive cycle is initiated.

The new sync is indicated at the COMMAND/DATA

SYNC (C/D SYNC) output and the TAKE DATA

output goes low

y. The C/D sync output will remain

in its valid state until a new sync is detected on a

subsequent word or until DECODER RESET (DEC

RST) or MRST goes low. A low at DEC RST or

MRST causes C/D SYNC to go low.

TAKE DATA remains low for 16 DSC periods during

which time the 16 serial data bits appear at the

SERIAL DATA OUTPUT (SDO). This data is

simultaneously loaded into the first-rank receive

makes the new data available at the output of the

second-rank receive register. This data remains

available until the next low-to-high transitions of

TAKE DATA. It is not reset or cleared by any other

signals. This data is applied to the D0 to D15 I/O

bus by setting DATA SELECT lines low.

After all data has been loaded into the receive

registers, the data is checked for odd parity. A low

VALID

WORD (VW)

output

z, indicates

successful

reception

word

without

any

Manchester or parity errors. For consecutive word

receptions, VW will go high again in 3 to 3.5µs. In

the absence of succeeding valid syncs, VW will

return high in 20µs. A DEC RST (low) at any time

will reset VW high.

All decoded commands, including RT ENABLE

(address recognition), BROADCAST and MODE

CODE are enabled internally by VW and remain

valid only as long as VW is low.

For 8-BIT l/O subsystems (D0 tied to D8, through

D7 tied to D15), data may be extracted in 8 BIT

bytes by selectively activating DATA SELECT 1 and

DATA SEL.ECT 2.

For serial data systems, SERIAL DATA OUTPUT is

available at the DSC rate from

y to z.

½ SYNC

FROM PREVIOUS WORD

UNDEFINED

VALID FOR CURRENT WORD

UNDEFINED

NOT VALID

FROM PREVIOUS WORD

OPTIONAL–HIGH = TRISTATE HI-Z AT D0 TO D15

NEW DATA

VALID

NOT VALID

VALID

NEW DATA

OSC

DATA IN

TAKE DATA

C/D SYNC

SDO

DECODE COMMANDS

SECOND-RANK REC’V

DATA SELECT

(see text)

Figure 5 – Receive Cycle Timing

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