Datasheet

MCP3909
DS22025C-page 24  2006-2012 Microchip Technology Inc.
5.0 SERIAL INTERFACE
DESCRIPTION
5.1 Dual Functionality Pin And Serial
Interface Overview
The MCP3909 device contains three serial modes that
are accessible by changing the pin functionality of the
NEG, F2, F1, and F0 pins to SDO, SCK, SDI and CS,
respectively.
These modes are entered by giving the MCP3909
device a serial command on these pins during a time
window after device reset or POR. During this window
of time, F2 acts as SCK, F1 acts as SDI and F0 acts
as CS
. Once a serial mode has been entered, the
device must be reset to disable mode functionality, or
change to another serial mode. This is done by using
MCLR pin or power on reset event.
During serial mode entry and the three serial modes,
data is clocked into the device on the rising edge of
SCK and out of the device on the falling edge of SCK.
The SPI data can be access at up to 20 MHz. This
speed enables quick data retrieval in between conver-
sion times. For 3-phase metering applications with
multiple ADCs, this fast communication is essential to
allow for power calculation windows between conver-
sions, as shown in Figure 5-3.
After a serial mode has been entered, all blocks of the
MCP3909 device are still operational. The PGA, A/D
converters, HPF, multiplier, LPF, and other digital sec-
tions are still functional, allowing the device to have
true dual functionality in energy metering systems.
FIGURE 5-1: Dual Functionality Pins for
the MCP3909.
FIGURE 5-2: Data Access between Data Ready Pulses using SPI Interface for a 3-phase System.
F
OUT0
D
GND
NEG/SDO
1
2
3
4
24
23
22
21
20
19
18
17
5
6
7
8
F
OUT1
NC
CLKOUT
CLKIN
DV
DD
HPF
AV
DD
NC
CH0+
CH0-
CH1-
CH1+
HF
OUT
16
9G0MCLR
15
14
10
11
G1
F0/C
S
REFIN/OUT
A
GND
13
12 F1/SDI F2/SCK
t
SAMPLE
t
LINE_CYC
SDO
DR
Phase A,B,C I & V Data
16 bits
DR
t
SAMPLE
IRQ
IRQ
x 6 ADCs