UR6HCPS2-SP40 Datasheet, PDF (12/22 Pages) Semtech Corporation – Converts PS/2 Data to Serial or SPI

ASYNCHRONOUS SERIAL INTERFACE (ASI) MODE
Baud rate:
The PS2Adapt^TM implements the ASI mode at fixed preselected Baud rates: 300bps, 600bps, 1200bps, 9600bps,
19200bps, 31250bps and 62500bps, depending on the Configuration pins’ state on power up. The IC can achieve
these standard Baud rates by using a 4MHz oscillator.
Protocol:
In Serial mode, the PS2Adapt^TM 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 UR6HCPS2-SP40 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 UR6HCPS2-SP40 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 UR6HCPS2-SP40 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 PS2Adapt^TM will try to start the transmission again.
_CTS
_RTS
TXD
1st
Byte
Last
Byte
t1
Figure 1: Serial Transmission Timing
Copyright Semtech, 2002-2001
12
DOC6-PS2-SP40-DS-102
www.semtech.com