REV. A

AD9874

–13–

SERIAL PERIPHERAL INTERFACE (SPI)

The serial peripheral interface (SPI) is a bidirectional serial port. It is used to load configuration information into the registers listed

below as well as to read back their contents. Table I provides a list of the registers that may be programmed through the SPI port.

Addresses and default values are given in hexadecimal form.

Table I. SPI Address Map

Address

Bit

(Hex)

Breakdown Width

Default Value Name

Description

POWER CONTROL REGISTERS

0x00

(7:0)

8

0xFF

STBY

Standby Control Bits (REF, LO, CKO, CK, GC, LNAMX, Unused,

and ADC).

0x01

(7:6)

2

0

LNAB

LNA Bias Current (0 = 0.5 mA, 1 = 1 mA, 2 = 2 mA, 3 = 3 mA).

(5:4)

2

0

MIXB

Mixer Bias Current (0 = 0.5 mA, 1 = 1.5 mA, 2 = 2.7 mA, 3 = 4 mA).

(3:2)

2

0

CKOB

CK Oscillator Bias (0 = 0.25 mA, 1 = 0.35 mA, 2 = 0.40 mA, 3 = 0.65 mA).

(1:0)

2

0

ADCB

Do not use.

0x02

(7:0)

8

0x00

TEST

Factory Test Mode. Do not use.

AGC

0x03

(7)

1

0

ATTEN

Apply 16 dB attenuation in the front end.

(6:0)

7

0x00

AGCG(14:8)

AGC Attenuation Setting (7 MSB of a 15-Bit Unsigned Word).

0x04

(7:0)

8

0x00

AGCG(7:0)

AGC Attenuation Setting (8 LSB of a 15-Bit Unsigned Word).

Default corresponds to maximum gain.

0x05

(7:4)

4

0

AGCA

AGC Attack Bandwidth Setting. Default yields 50 Hz raw loop bandwidth.

(3:0)

4

0

AGCD

AGC Decay Time Setting. Default is decay time = attack time.

0x06

(7)

1

0

AGCV

Enable digital VGA to increase AGC range by 12 dB.

(6:4)

3

0

AGCO

AGC Overload Update Setting. Default is slowest update.

(3)

1

0

AGCF

Fast AGC (Minimizes resistance seen between GCP and GCN).

(2:0)

3

0

AGCR

AGC Enable/Reference Level (Disabled, 3 dB, 6 dB, 9 dB, 12 dB, 15 dB

below Clip).

DECIMATION FACTOR

0x07

(7:5)

3

Unused

(4)

1

0

K

Decimation Factor = 60

(M + 1), if K = 0; 48

(M + 1), if K = 1.

(3:0)

4

4

M

Default is Decimate-by-300.

LO SYNTHESIZER

0x08

(5:0)

6

0x00

LOR(13:8)

Reference Frequency Divisor (6 MSB of a 14-Bit Word).

0x09

(7:0)

8

0x38

LOR(7:0)

Reference Frequency Divisor (8 LSB of a 14-Bit Word).

0x0A

(7:5)

3

0x5

LOA

“A” Counter (Prescaler Control Counter).

(4:0)

5

0x00

LOB(12:8)

“B” Counter MSB (5 MSB of a 13-Bit Word).

Default LOA and LOB values yield 300 kHz from 73.35 MHz to 2.25 MHz.

0x0B

(7:0)

8

0x1D

LOB(7:0)

“B” Counter LSB (8 LSB of a 13-Bit Word).

0x0C

(6)

1

0

LOF

Enable fast acquire.

(5)

1

0

LOINV

Invert charge pump (0 = source current to increase VCO frequency).

(4:2)

3

0

LOI

0.625 mA.

(1:0)

2

3

LOTM

Manual Control of LO Charge Pump (0 = Off, 1 = Up, 2 = Down,

3 = Normal).

0x0D

(5:0)

4

0x0

LOFA(13:8) LO Fast Acquire Time Unit (6 MSB of a 14-Bit Word).

0x0E

(7:0)

8

0x04

LOFA(7:0)

LO Fast Acquire Time Unit (8 LSB of a 14-Bit Word).