User's Manual

UART MODE 4

UART Mode 4 incorporates level sensitive flow control on the TX channel and requires no flow control

on the RX channel, supporting 115200 baud. The use of level sensitive flow control signals enables

higher data rates with the option of using a reduced set of the flow control signals; however, with the

companion processor must negate UART_TX_CTSn prior to the end of the packet and wait at least

tRX_RTS to RX_CTS between sending packets. See the UART AC Characteristics section for complete

timing specifications. Packets are HDLC encoded with one stop bit and no parity bit. The use of the RX

flow control signals (UART_RX_RTSn and UART_RX_CTSn) for Mode 4 are optional. The flow control

signals for the TX channel are shown in Figure 20. UART Mode 4 Transmit Flow Control. Transfers are

initiated by WSM2400 asserting UART_TX_RTSn. The UART_TX_CTSn signal may be actively driven by

the companion processor when ready to receive a packet or UART_TX_CTSn may be tied low if the

companion processor is always ready to receive a packet. After detecting a logic ‘0’ on UART_TX_CTSn

WSM2400 sends the entire packet. Following the transmission of the final byte in the packet WSM2400

negates UART_TX_RTSn and waits for a minimum period defined in the UART AC Characteristics section

before asserting UART_TX_RTSn again. For details on the timing of the UART protocol, see the UART AC

Characteristics section.

Figure 20. UART Mode 4 flow control

CLI UART

The Command Line Interface (CLI) UART port is a two wire protocol (TX and RX) that operates at a fixed

9600 baud rate with one stop bit and no parity. The CLI UART interface is intended to support command

line instructions and response activity.

AUTONOMOUS MAC

WSM2400 was designed as a system solution to provide a reliable, ultralow power, and secure network.

A reliable network capable of dynamically optimizing operation over changing environments requires

solutions that are far too complex to completely support through hardware acceleration alone. As

described in the Precision Timing section, proper time management is essential for optimizing a solution

that is both low power and reliable. To address these requirements WSM2400 includes the autonomous

MAC, which incorporates a coprocessor for controlling all of the time critical radio operations. The

autonomous MAC provides two benefits: first, preventing variable software latency from affecting