Hardware Configurations
The full implementation of ANT is represented in Fig. Hw1.
The line SRQ (Service ReQuest) need not be present, but it can be extremely useful for advanced operation.
MNC is the Master Network Controller. It can be a microcontroller board with USART but it can also be (and often is, especially during application developing and system configuration) a PC. In this case the SRQ line, if present, connects to the CTS signal of the TTL RS232 adapter that also connects to RX and TX on the MNC side.
SND are Slave Networked Devices. At present they can be either ATMEGA328 or ATtiny2313 microcontrollers. TX and RX connect to the USART pins and SRQ to another pin (to be specified).
Operation of the system proceeds as follows.
All SNDs run their respective main codes. ANT provides for transparently managing communication and interaction between MNC and SNDs.
Normally (in the absence of the SRQ line or in the absence of a Service ReQuest by the Slaves) communication is initiated by the MNC according to the following procedure:
- MNC sends a BREAK
- All SNDs disconnect their TX terminal from the network (actually in normal operation there may only be 1 or none TX connected to the network at any given time);
- MNC sends the address of the SND to be connected to the network
- All SNDs receive the address. Only the one with the internal address equal to that sent by the MNC connects its TX to the network.
- Communication between MNC and the selected SND can now proceed very much like as the other SNDs were not present in the network.
If the MNC sends the special Broadcast address (0xFF), all SNDs will start listening (that is receiving and interpreting following messages from the MNC) but none of them will connect its own TX to the network.
If the SRQ line is present, it is assumed that the MNC monitors the SRQ line. Note that the SQR outputs from the SNDs are in high impedance at rest. The SND that requests a service activates the output bringing it to LOW level ( the SRQ input at the MNC side is assumed to be pulled up). More than one SND can assert SRQ at the same time. When the MNC recognizes that SRQ has been asserted, it must initiate a polling for finding out which (possibly more than one) SNDs have activated SRQ. Note that during this polling, the SRQ line can be used for simplifying the polling itself with a mechanism similar to the plug and play discovery algorithm in ISA (not sure, actually, that it was ISA) interface.