LTC6820
operaTion
Multidrop
n
n
The SPI slaves must be addressable, because they will
all see the same CS signal (as decoded by each slave
LTC6820).
Multipleslavescanbeconnectedtoasinglemasterbycon-
nectingtheminparallel(multidropconfiguration)alongone
cable.AsshowninFigure16,thecableshouldbeterminated
only at the beginning (master) and the end. In between, the
additionalLTC6820’sandtheirassociatedslavedeviceswill
be connected to “stubs” on the cable. These stubs should
bekeptshort,withaslittlecapacitanceaspossible,toavoid
degrading the termination along the cable.
When not addressed, the slave SDO must remain high.
When a slave is not addressed, its LTC6820 will not trans-
mit data pulses as long as MISO (the SPI device’s SDO)
remainshigh. Thiseliminatesthepossibilityforcollisions,
as only the addressed slave device will ever be returning
data to the master.
The multidrop scheme is only possible if the SPI slaves
have certain characteristics:
MASTER
LTC6820
MSTR
SLAVE 1
LTC6820
MSTR
IP
IP
1
MOSI
MISO
SCK
CS
SDO
SDI
SCK
CS
SDI
SDO
SCK
CS
MOSI
MISO
IM SCK
CS
R
M
IM
1
1
LTC6820
MSTR
SLAVE 2
IP
2
SDI
SDO
SCK
CS
MOSI
MISO
IM SCK
CS
2
2
LTC6820
MSTR
SLAVE 3
IP
3
SDI
SDO
SCK
CS
MOSI
R
M
MISO
IM SCK
CS
3
3
6820 F16
Figure 16. Multidropping Multiple Slaves on a Single Cable
6820f
18
Linear [ Linear ]
