EM357-RTR datasheet(27/240 Pages) ETC2

27 / 240 page

EM351 / EM357

4-2

120-035X-000D

Preliminary

nTX_ACTIVE is the alternate function of PC6. See Chapter 7 GPIO for details of the alternate GPIO functions.

The digital I/O that provide these signals have a 4 mA output sink and source capability.

4.3

Calibration

The Ember software calibrates the radio using dedicated hardware resources.

4.4

Integrated MAC Module

The EM35x integrates most of the IEEE 802.15.4-2003 MAC requirements in hardware. This allows the ARM

CortexTM-M3 CPU to provide greater bandwidth to application and network operations. In addition, the

hardware acts as a first-line filter for unwanted packets. The EM35x MAC uses a DMA interface to RAM to

further reduce the overall ARM

® CortexTM-M3 CPU interaction when transmitting or receiving packets.

When a packet is ready for transmission, the Ember software configures the Tx MAC DMA by indicating the

packet buffer RAM location. The MAC waits for the backoff period, then switches the baseband to Tx mode

and performs channel assessment. When the channel is clear the MAC reads data from the RAM buffer,

calculates the CRC, and provides 4-bit symbols to the baseband. When the final byte has been read and sent

to the baseband, the CRC remainder is read and transmitted.

The MAC is in Rx mode most of the time. In Rx mode various format and address filters keep unwanted packets

from using excessive RAM buffers, and prevent the CPU from being unnecessarily interrupted. When the

reception of a packet begins, the MAC reads 4-bit symbols from the baseband and calculates the CRC. It then

assembles the received data for storage in a RAM buffer. Rx MAC DMA provides direct access to RAM. Once the

packet has been received additional data, which provides statistical information on the packet to the Ember

software, is appended to the end of the packet in the RAM buffer space.

The primary features of the MAC are:

CRC generation, appending, and checking

Hardware timers and interrupts to achieve the MAC symbol timing

Automatic preamble and SFD pre-pending on Tx packets

Address recognition and packet filtering on Rx packets

Automatic acknowledgement transmission

Automatic transmission of packets from memory

Automatic transmission after backoff time if channel is clear (CCA)

Automatic acknowledgement checking

Time stamping received and transmitted messages

Attaching packet information to received packets (LQI, RSSI, gain, time stamp, and packet status)

IEEE 802.15.4-2003 timing and slotted/unslotted timing

4.5

Packet Trace Interface (PTI)

The EM35x integrates a true PHY-level PTI for effective network-level debugging. It monitors all the PHY Tx

and Rx packets between the MAC and baseband modules without affecting their normal operation. It cannot

be used to inject packets into the PHY/MAC interface. This 500 kbps asynchronous interface comprises the

frame signal (PTI_EN, PA4) and the data signal (PTI_DATA, PA5). PTI is supported by Ember’s InSight

Development tools.

4.6

Random Number Generator

Thermal noise in the analog circuitry is digitized to provide entropy for a true random number generator

(TRNG). The TRNG produces 16-bit uniformly distributed numbers. The Ember software uses the TRNG to seed

a pseudo random number generator (PRNG). The TRNG is also used directly for cryptographic key generation.

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