The PC2070 receives TMP paging packets via Port B
and Port D.
Port B is dedicated to the Lantronix which is a TCP
to serial device. The Netcomm modem transmits packets from the Vodafone WAN
to the TCP port.
Port D is dedicated to the Modmax serial to WAN
modem.
Usually only one device exists at any one time
however the CPU will accept messages from either port and has separate
buffers for both ports. Thus the two ports can operate independently.
The PC2070 runs 24/7 over the M2M network as a TCP
connection. By its nature the TCP device is a connectionless protocol,
however there are interruptions to the wireless network for many reasons and
the virtual link will be lost. During these interruptions the M2M link will
loose its TCP connection and will be required to re-establish it.
It is important that the PC2070 is aware of the link
failure and can re-establish the link or in the case where the PC2070 is not
aware another hardware based system initiates the link reconnection.
The simplest way to re-establish the M2M link is to
re-power all the M2M link components. This is the safest however it is also
the longest.
Powering down some of the components is quicker
however the CPU must be aware of which component is compromised.
Timers:
The PC2070 system monitors the M2M link and resets
two timers associated with re-powering the system on the detection of the
M2M link failure.
CPU Timer:
The CPU timer resets on the receipt of valid packets
from the WAN device. If the packet is not recognised as part of the protocol
from the Gateway to the PC2070 then the timer is not reset. The CPU timer is
set to 90 seconds and the Gateway sends packets every 20 seconds.
When the CPU timer expires the reset circuit is
activated and the CPU will restart. This is useful if the system was
confused or lost in a loop. It is not completely safe as the memory is
static and its possible that some variables are left at the same value and
the program may not restart as if it was re-powered. The reset however is
quick and the CPU can recover within seconds.
One disadvantage of the reset is the CPU at the
start of the reset will toggle off the power to the Lantronix and the
Netcomm modem. The diagram below represents the timer components.
RX Port Timer:
The Port B timer is a hardware device. It is reset
when data appears on the Rx line. The timer is set approximately to 10
minutes by a capacitor-resistor timing circuit. The advantage of this
circuit is it will re-power the CPU as well as the Lantronix and Netcomm
modem. It assumes the CPU is compromised as well as the modem and Lantronix
device.
The Port B timer is the catch-all device. It will
continue to cycle the system on and off every 10 minutes until data appears
on Port B. The diagram below represents the timer components.
