CMX910 datasheet(23/61 Pages) CMLMICRO

23 / 61 page

AIS Baseband Processor

CMX910

D/910/6

CSTDMA_Threshold register: 16-bit write only.

C-BUS Address $26

All bits cleared to 0 on reset.

Bit:

CSTDMA signal strength threshold

The value in the CSTDMA_threshold register is used when attempting a transmission with

CSTDMA enabled. At the beginning of the slot in which data is to be transmitted, typically just

before the PA is ramped up, the received signal strength in the selected CSTDMA channel (Rx1

or Rx2) is measured. If this exceeds the value in the CSTDMA_threshold register, the

transmission is aborted and a TxDone interrupt is generated. Otherwise, transmission proceeds

normally. Note: the value written to the CSTDMA_Threshold register must be between 0 and

32767 ($7FFF).

The received signal strength is calculated by accumulating the I/Q vector magnitudes at each

sample point (i.e. every 20.833µs) between the CSTDMA_START and CSTDMA_END points, as

defined in the Tx Event Sequence table (see section 5.5.5). Before being added to the running

total, each vector magnitude is multiplied by a fixed gain of 0.4117 and a user-programmable gain

“CSTDMA_gain” of between 0 and 1 (this is set up using a special command function, see section

5.12). In the case of overflow, the accumulated signal strength value saturates at 32767 ($7FFF).

The total accumulated signal strength value is given by:

∑

⎟

⎠

⎞

⎜

⎝

⎛

END

CSTDMA

START

CSTDMA

gain

CSTDMA

strength

signal

CSTDMA

4117

For the purpose of calculating the CSTDMA signal strength, the signed 16-bit I and Q vector

values are taken directly from the output of the selected channel’s Σ-Δ ADCs, prior to passing

through the channel filters. With a DC voltage of ±1.7V (differential) applied to the input of the I or

Q ADC, the corresponding I or Q ADC output will be approximately ±15000.

CMX910 Datasheet(PDF) 23 Page - CML Microcircuits

CMX910 Datasheet(HTML) 23 Page - CML Microcircuits

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61

Datasheet Download

Link URL