EM260-BBRD-128K-USART-R Ember, EM260-BBRD-128K-USART-R Datasheet - Page 35

• Manufacturer Part Number: EM260-BBRD-128K-USART-R
• Description: EM260 BREAKOUT BOARD
• Manufacturer: Ember
• Type: Transceiver, 802.15.4/ZigBeer

Specifications of EM260-BBRD-128K-USART-R

• Frequency: 2.4GHz
• For Use With/related Products: EM260
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 636-1026

6 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 Ember’s 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 the UART Gateway Protocol Reference, 120-3010-000.
Ember 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.
The UART hardware interface uses the following EM260 signals:
•
•
•
Serial data: TXD and RXD
Flow control: nRTS and nCTS (optional)
Reset control: nRESET
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.
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.
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.
HOST
Figure 13. UART Interface Signals
TXD
RXD
nCTS
nRTS
GPIO
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Flow Control
Data
nRESET
RXD
TXD
nRTS
nCTS
EM260
EM260
120-0260-000J