MA28151

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Figure 6: Transmission Format

Figure 7: Receive Format

3.6 SYNCHRONOUS MODE (TRANSMISSION)

The TxD output is continuously high until the CPU sends its

first character to the MA28151 which usually is a SYNC

character. When the

CTS line goes low, the first character is

serially transmitted out. All characters are shifted out on the

falling edge of

TxC. Data is shifted out at the same rate as the

TxC.

Once transmission has started, the data stream at the TxD

output must continue at the

TxC rate. If the CPU does not

provide the MA28151 with a data character before the

MA28151 Transmitter Buffers become empty, the SYNC

characters (or character if in single SYNC character mode) will

be automatically inserted in the TxD data stream. In this case,

the TxEMPTY does not go low when the SYNC is being shifted

out (see figure 8). The TxEMPTY pin is internally reset by a

data character being written into the MA28151.

3.7 SYNCHRONOUS MODE (RECEIVER)

In this mode character synchronisation can be internally or

externally achieved. If the SYNC mode has been

programmed, ENTER-HUNT command should be included in

the first command instruction word written. Data on the RxD

pin is then sampled on the rising edge of

RxC. The content of

the Rx buffer is compared to every bit boundary with the first

SYNC character until a match occurs.

If the MA28151 has been programmed for two SYNC

characters, the subsequent received character is also

compared; when both SYNC characters have been detected,

the USART ends the HUNT mode and is in character

synchronization. The SYNDET pin is then set high, and is reset

automatically by a STATUS READ. If parity is programmed,

SYNDET will not be set until the middle of the parity bit, instead

of the middle of the last data bit.

In the external SYNC mode, synchronization is achieved

by applying a high level on the SYNDET pin, thus forcing the

MA28151 out of the HUNT mode. The high level can be

removed after one

RxC cycle. An ENTER HUNT command

has no effect in the asynchronous mode of operation.

Figure 8: Sync Character Insertion

PARITY BIT

DATA CHARACTER

STOP BITS

START BIT

DATA CHARACTER

ASSEMBLED SERIAL DATA OUTPUT (TxD)

CPU BYTE (5-8 BITS/CHARACTER)

PARITY BIT

DATA CHARACTER

STOP BITS

START BIT

DATA CHARACTER

SERIAL DATA INPUT (RxD)

CPU BYTE (5-8 BITS/CHARACTER) (See Note Below)

NOTE: If character length is defined as 5, 6 or 7 bits the unused bits are set to zero.