UR7HCTS2-S840 Datasheet, PDF (8/16 Pages) Semtech Corporation – High-Performance, Low Power Touch Screen Controller/Digitizer

ASYNCHRONOUS SERIAL INTERFACE (ASI) MODE
Baud rate:
The ScreenCoder^TM SPI/Serial transmits data at 19200 Baud, using the recommended 4MHz oscillator.
Protocol:
In Serial mode, the ScreenCoder^TM SPI/Serial supports transmission in one direction only (IC to Host). The IC starts
the transmission to the system when it has mouse/keyboard package pending. The data format is one start bit, 8
data bits, no parity and one stop bit.
1. The ScreenCoder^TM SPI/Serial asserts _CTS low to indicate that a packet transfer will start.
2. The Host asserts _RTS low to indicate that it is ready to receive data.
_RTS low means that system can receive data (e.g. UART is operational).
3. The UR7HCTS2-S840 places data on TXD line when it detects the _RTS low.
4. When one package is successfully transmitted, the IC raises _CTS.
Notes on the Protocol:
To assure fast transmission, the system must assert _RTS low as soon as possible. If the system is ready to receive
the data, it doesn't have to raise _RTS between packages.
The UR7HCTS2-S840 checks _RTS after every byte transmission. If _RTS returns to high, it means that the
transmission was unsuccessful. The IC will raise _CTS to abort the transmission and the entire package will be re-
transmitted.
The maximum time of T1 is 10ms. If the system cannot assert _RTS low after 10ms of _CTS low, the IC will raise
_CTS to abort the transmission request. After that, the ScreenCoder^TM SPI/Serial will try to start the transmission
again.
_CTS
_RTS
TXD
1st
Byte
Last
Byte
t1
Figure 1: Serial Transmission Timing
Copyright Semtech 2000-2001
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DOC7-TS2-S840-DS-102
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