Datasheet

CS
DOUT
SCLK
DIN
MSP430
CS
SCLK
DIN1
DOUT1
U1
CS
SCLK
DIN2
DOUT2
U2
PGA116/PGA117 PGA116/PGA117
10 Am
PGA112
PGA113
DOUT
DIO
DIN
SERIAL DIGITAL INTERFACE: SPI
CS
DOUT
SCLK
DIN
MSP430
CS
SCLK
DIN1
DOUT1
U1
CS
SCLK
DIO
U2
PGA116/PGA117 PGA112/PGA113
PGA112 , , PGA113
PGA116 , PGA117
www.ti.com ............................................................................................................................................ SBOS424B – MARCH 2008 – REVISED SEPTEMBER 2008
On the PGA112/PGA113, there are digital output and used (see Table 4 ) to ensure that data are written or
digital input gates both internally connected to the read in the proper sequence. There is a special
DIO pin. DIN is an input-only gate and DOUT is a daisy-chain NOP command (No OPeration) which,
digital output that can give a 3-state output. The DIO when presented to the desired device in the
pin has a weak 10 µ A pull-down current source to daisy-chain, causes no changes in that respective
prevent the pin from floating in systems with a device. Detailed timing diagrams for daisy-chain
high-impedance SPI DOUT line. When CS is high, operation are shown in Figure 65 through Figure 67 .
the state of the internal DOUT gate is
high-impedance. When CS is low, the state of DIO
depends on the previous valid SPI communication;
either DIO becomes an output to clock out data or it
remains an input to receive data. This structure is
shown in Figure 60 .
Figure 61. Daisy-Chain Read/Write Configuration
The PGA112/PGA113 can be used as the last device
in a daisy-chain as shown in Figure 62 if write-only
communication is acceptable, because the
PGA112/PGA113 have no separate DOUT pin to
connect back to the microcontroller DIN pin in order
to read back data in this configuration.
Figure 60. Digital I/O Structure — PGA112/PGA113
DAISY-CHAIN COMMUNICATIONS
To reduce the number of I/O port pins used on a
microcontroller, the PGA116/PGA117 support SPI
Figure 62. Daisy-Chain Write-Only Configuration
daisy-chain communications with full read/write
capability. A two-device daisy-chain configuration is
shown in Figure 61 , although any number of devices
can be daisy-chained. The SPI daisy-chain
communication uses a common SCLK and CS line
for all devices in the daisy chain, rather than each
device requiring a separate CS line. The daisy-chain
mode of communication routes data serially through
each device in the chain by using its respective DIN
and DOUT pins as shown. Special commands are
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Product Folder Link(s): PGA112 PGA113 PGA116 PGA117