EM260-RTR datasheet(35/50 Pages) SILICONIMAGE

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EM260

Page 35

120-0260-000M Rev 1.1

UART Gateway Protocol

The UART Gateway protocol is designed for network gateway systems in which the host processor is running a

full-scale operating system such as embedded Linux or Windows. The host sends EmberZNet Serial Protocol

(EZSP) commands to the UART interface using the Ember Asynchronous Serial Host (ASH) protocol. The EZSP

commands are the same as those used in the SPI protocol, but the SPI protocol is better suited for resource-

constrained microcontroller hosts since ASH uses considerably more host RAM and program storage.

ASH implements error detection/recovery and tolerates latencies on multi-tasking hosts due to scheduling and

I/O buffering. The ASH protocol is described in detail in document UG101, UART Gateway Protocol Reference.

Silicon Labs supplies ASH host software in source form compatible with Linux and Windows. In most cases it

will need only a few simple edits to adapt it to a particular host system.

Figure 13. UART Interface Signals

The UART hardware interface uses the following EM260 signals:



Serial data: TXD and RXD

The ASH protocol sends data in both directions, so both TXD and RXD signals are required. An external

pull-up resistor should be connected to TXD to avoid data glitches while the EM260 is resetting.



Flow control: nRTS and nCTS (optional)

ASH uses hardware handshaking for flow control: nRTS enables transmission from the host to the

EM260, and nCTS enables EM260 transmissions to the host. If the host serial port cannot support

RTS/CTS, XON/XOFF flow control may be used instead. But, XON/XOFF will deliver slightly lower

performance.

When using hardware flow control, the EM260’s nRTS must be able to control host serial output.

However, in many gateway systems, the host will not need to throttle transmission by the EM260. In

those systems nCTS may be left unconnected since it has an internal pull-down and will be

continuously asserted.



Reset control: nRESET

The host must be able to reset the EM260 to run the ASH protocol. The best way to do this is to use a

host output connected to nRESET. If this is not feasible, the host can send a special ASH frame that

requests the EM260 to reboot, but this method is less reliable than asserting nRESET and is not

recommended for normal use.

RXD

TXD

nRTS

nCTS

nRTS

GPIO

nRESET

HOST

EM260

Data

Flow Control

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