DA7838.002

20 September, 2000

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Timings between synchronous clocks and data are shown below. Note that absolute delays depend on the speed of

the data transmission.

If pin TSL = 1 (Automatic synchronous sampling timing)

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The synchronous start-stop character, TDI (transmitter

data input), is read into the Tx buffer. When the

character is available the data bits are transferred as

TDO (transmitter data output) with the synchronous

timing signal TXC (transmitter clock). The bit rate of TDI

must be the same as the TDO rate within -2.5%...+1%

or -2.5%...+2.3% tolerance depending on XESR

(extended signalling rate) signal. The transmitter adds

extra stop bits to the synchronous data stream, if TDI is

slower than TDO. The over speed is handled by

deleting one stop bit in every 8th character at maximum

in the synchronous output data TDO. When extended

signal rate (XESR = 0) is used 4th stop bit may be

deleted. When the transmitter detects a break signal( at

least M bits of start polarity, where M is length of

character), it sends 2M + 3 bits of start - polarity to

TDO. If the break is longer than 2M + 3 bits, then all bits

are transferred to TDO. After a break signal, at least 2M

bits of stop polarity must be transmitted before sending

further data.

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The synchronous RDI (receiver data input) is buffered

to recognise the stop and start bits. If a missing stop bit

is detected, it is added to the RDO (receiver data

output). In this case the stop bits are shortened 12.5%

(25% if XESR = 0) during each character. When the

receiver gets at least 2M + 3 bits of start polarity, it does

not add stop bits to RDO. This enables the break signal

to go through the buffer.

An alternative method to handle the over speed in

asynchronous data is to boost synchronous timing TXC

and RXC by 1-2%. In this mode XHST (higher speed

timing) = 0. In this case there is no need to delete any

stop bits in the transmitter buffer. The break signal goes

through unchanged. On the receiver side the

synchronous data, RDI, is transferred directly to the

asynchronous output RDO with RXC.

T

RXC

T2

T3

RXC

RDI

TXC

TDO

T

TXC

delay

T1