Echelon FT 3150 Smart Transceiver - Manual (Page 21)

FT 3120 / FT 3150 Smart Transceiver Data Book 15
Memory Allocation
• Unique 48-bit Neuron ID.
• Optional user-written application code and data tables.
All but 8 bytes of the EEPROM can be written under program control using an on-chip charge pump to generate the
required programming voltage. The charge pump operation is transparent to the user. The remaining 8 bytes are
written during manufacture, and contain a unique 48-bit identifier for each part called the Neuron ID, plus 16 bits for
the device code of the chip manufacturer. Each byte in the EEPROM region may be written up to 10,000 times. For
both the FT Smart Transceivers, the EEPROM stores the installation-specific information such as network addresses
and communications parameters. For the FT 3120 Smart Transceiver, the EEPROM also stores the application
program generated by the LonBuilder or NodeBuilder development tools. The application code for the FT 3150
Smart Transceiver may be stored either on-chip in the EEPROM memory or off-chip in external memory depending
on the size of the application code. See Table 2.6 for available EEPROM space.
For all write operations to the internal EEPROM, the Neuron firmware automatically compares the value in the
EEPROM location with the value to be written. If the two are the same, the write operation is not performed. This
prevents unnecessary write cycles to the EEPROM, and reduces the average EEPROM write cycle latency.
When the FT Smart Transceiver is not within the specified power supply voltage range, a pending or on-going
EEPROM write is not guaranteed. The FT Smart Transceiver contains a built-in low-voltage interruption (LVI)
circuit that holds the chip in reset when V
CC
is below a certain voltage. See the FT 3120 and FT 3150 Smart
Transceiver Datasheet for LVI trip points. This prevents EEPROM data corruption, although in some cases,
additional external protection may be appropriate. See section , RESET Pin, for more information on LVI circuitry.
In the event of a fault, the on-chip EEPROM of the FT 3150 Smart Transceiver can be reset to its factory default state
by executing the EEBLANK program. To do so, program the EEBLANK.NRI file into an external memory device,
temporarily replace the external ROM or flash for the application with the chip that has EEBLANK.NRI loaded, and
power up the device.
After some time, the service LED of the device should come on solid, indicating that the EEPROM has been blanked.
Then replace the original application ROM or flash. The EEBLANK.NRI file is distributed with the LonBuilder 3.01
(Service Pack 5), NodeBuilder 1.5 (Service Pack 8 or greater), and NodeBuilder 3 (Service Pack 1 or greater)
development tools. The file may also be downloaded from the developer’s toolbox located on the Echelon website
(www.echelon.com). Versions of EEBLANK.NRI distributed before these Service Packs should not be used with
the FT 3150 Smart Transceiver.
The set_eeprom_lock() function can also be used for additional protection against accidental EEPROM data
corruption. This function allows the application program to set the state of the lock on the checksummed portion of
the EEPROM. Refer to the Neuron C Reference Guide for more information.
The internal EEPROM of a FT Smart Transceiver will contain a fixed amount of overhead and a network image
(configuration), in addition to user code and user data. The following table shows the maximum amount of EEPROM
space available for user code and user data assuming a minimally-sized network image. Also shown is the minimum
segment size for user data. Constant data is assumed to be part of the code space.
Table 2.6 Memory Usage
EEPROM must be allocated in increments of the device's segment size, the smallest unit of EEPROM that can be
allocated for variable space. For example, if there are three 3-byte variables used, there must be 9 bytes of variable
space. For an FT 3120 Smart Transceiver, this would result in the allocation of 16 bytes for variable space, as 16
bytes is the lowest increment of the device segment size (8 bytes) that can store the three 3-byte variables. For an FT
3150 Smart Transceiver, this would result in the allocation of 10 bytes for variable space, as 10 bytes is the lowest
increment of the device segment size (2 bytes) that can store the three 3-byte variables.
Device Firmware Version
EEPROM Space
(Bytes)
Segment Size
(Bytes)
FT 3120 Smart Transceiver 13 3969 8
FT 3150 Smart Transceiver 13 384 2