MA28151 datasheet(8/22 Pages) DYNEX

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MA28151

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Parity error and overrun error are both checked in the same

way as in the Asynchronous Receive mode. Parity is checked

when not in HUNT, regardless of whether the Receiver is

enabled or not.

The CPU can command the receiver to enter the HUNT

mode if synchronisation is lost. This will also set all the used

character bits in the buffer to a one thus preventing a possible

false SYNDET caused by data that happens to be in the Rx

buffer at ENTER HUNT time.

Note: the SYNDET flip-flop is reset at each Status Read,

regardless of whether internal or external SYNC has been

programmed. This does not cause the MA28151 to return to

the HUNT mode. When in SYNC mode, but not in HUNT, Sync

Detection is still functional, but only occurs at the known word

boundaries. Thus, if one Status Read indicates SYNDET and a

second Status Read also indicates SYNDET, then the

programmed SYNDET characters have been received since

the previous Status Read. (If double character sync has been

contiguously received to gate a SYNDET indication). When

external SYNDET mode is selected, internal Sync Detect is

disabled, and the SYNDET flip-flop may be set at any bit

boundary.

3.9 DATA FORMAT, SYNCHRONOUS MODE

DATA CHARACTERS

ASSEMBLED SERIAL DATA OUTPUT (TxD)

SYNC CHAR 1

SYNC CHAR 2

DATA CHARACTERS

Figure 9: Receive Format, Synchronous Mode

Figure 10: Data Format, Synchronous Mode

DATA CHARACTERS

CPU BYTES (5-8 BITS/CHARACTER)

SYNC CHAR 1

SYNC CHAR 2

DATA CHARACTERS

3.8 MODE INSTRUCTION FORMAT, SYNCHRONOUS MODE

SS ES EP PEN L2 L1

CHARACTER LENGTH

BITS

PARITY ENABLE AND SENSE

1 = ENABLE 0 = DISABLE

1 = EVEN 0 = ODD

EXTERNAL SYNC DETECT

1 = SYNCDET IS AN INPUT

0 = SYNCDET IS AN OUTPUT

SINGLE CHARACTER SYNC

1 = SINGLE SYNC CHAR.

0 = DOUBLE SYNC CHAR.

Figure 11: Mode Instruction Format, Synchronous Mode

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