User's Manual

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M2x40 Mote Datasheet Dust Networks™ 14
Timeouts T1, T2, and T3 are defined as follows (refer to Error! Reference source not found. for values):
T1: interbyte_timeout—Maximum time between the transmit module sending a byte and the receiving module
acknowledging the byte using CTS (requests the next byte).
T2: interpacket_delay—For communications into the mote, the minimum time after the mote receives the last byte of a
packet before it can start receiving the next packet. For communications out of the mote, the minimum time between the
mote receiving acknowledgement of the last byte reception (or timeout) and the mote driving MT_RTS
¯¯¯¯¯¯¯
to request to send
another packet.
T3: min_strobe_length—The minimum length of time that CTS must be held active to be recognized by the receiver.
In idle mode or upon expiration of the interbyte_timeout, the transmit side treats CTS as level triggered (MT_RTS
¯¯¯¯¯¯¯
is
disregarded in case of local serial packets). After transfer of the first byte of a packet, the meaning of CTS signal is changed
to a byte acknowledgement strobe, active on a falling edge. In other words, CTS becomes a request signal for the next byte of
a packet. This acknowledgement strobe will occur for all packets (both local and network packets). Whenever timeouts T1 or
T2 occur, the packet is discarded and both sides switch to idle mode and start hunting for the next HDLC packet, assuming
CTS active low. If a packet is transferred completely, the interbyte_timeout after the last byte naturally takes care of
switching to idle mode.
8.3.2.2 Data Flow Out of the Mote Serial Port
Figure 9 illustrates the process that the mote uses to transmit serial data:
1. The mote ensures the interpacket_delay time has passed since the last transmission.
2. The mote drives MT_RTS
¯¯¯¯¯¯¯
to active, waits for a falling edge on SP_CTS
¯¯¯¯¯¯¯
. Timeout is defined as ack_delay (see Error!
Reference source not found.), and is long enough to handle the worst-case response.
3. If the mote times out before the SP_CTS
¯¯¯¯¯¯¯
becomes active, the mote restores MT_RTS
¯¯¯¯¯¯¯
to inactive and drops the packet.
4. If SP_CTS
¯¯¯¯¯¯¯
is active, then the mote transmits the first byte and follows the CTS byte-level handshaking rules for
subsequent bytes.
5. MT_RTS
¯¯¯¯¯¯¯
is restored to inactive after the ack_delay timeout has expired.
Figure 9 Packet Transmission from Mote
8.3.2.3 Data Flow Into the Mote Serial Port
Figure 10 illustrates the process the mote uses to receive serial data.
The mote may receive serial packets for local commands (not intended for wireless transmission) at any time regardless of
the MT_CTS
¯¯¯¯¯¯¯
status.
The mote signals its readiness to receive serial packets for wireless transmission (serial payload command 0x80) by driving
MT_CTS
¯¯¯¯¯¯¯
active low. The mote will drive MT_CTS
¯¯¯¯¯¯¯
low within interpacket_delay time (see Error! Reference source not
found.) after the transmission of the last packet.