GS3140 Datasheet, PDF (29/40 Pages) Semtech Corporation – Multi-Rate Adaptive 3G SDI Equalizer

Read access is the same as the above except in step 1 the Command Word is set for read
access (R/W = 1).
Note: The UNIT ADDRESS field of the Command Word must always match
DEVICE_UNIT_ADDRESS for an access to be accepted by the device. Changing
DEVICE_UNIT_ADDRESS to a value other than 0 is only required if multiple devices are
connected to a single chip select (in Loop-Through or Bus-Through configuration).
4.11.10 Setting a Device Unit Address
Multiple (up to 32) GS3140 devices can be connected to a common Chip Select (CS) in
Loop-Through or Bus-Through operation.
To ensure that each device selected by a common CS can be separately addressed, a
unique Unit Address must be programmed by the host processor at start-up as part of
system initialization or following a device reset.
Note: By default at power up or after a device reset, the DEVICE_UNIT_ADDRESS of each
device is set to 0h and the SDIN → SDOUT non-clocked loop-through for each device is
enabled.
These are the steps required to set the DEVICE_UNIT_ADDRESS of devices in a chain to
values other than 0:
1. Write to Unit Address 0 selecting HOST_CONF_REG_0 (ADDRESS = 0), with the
GSPI_LINK_DISABLE bit set to 1 and the DEVICE_UNIT_ADDRESS field set to 0. This
disables the direct SDIN → SDOUT non-clocked path for all devices on chip select.
2. Write to Unit Address 0 selecting HOST_CONF_REG_0 (ADDRESS = 0), with the
GSPI_LINK_DISABLE bit set to 0 and the DEVICE_UNIT_ADDRESS field set to a
unique Unit Address. This configures DEVICE_UNIT_ADDRESS for the first device in
the chain. Each subsequent such write to Unit Address 0 will configure the next
device in the chain. If there are 32 devices in a chain, the last (32nd) device in the
chain must use DEVICE_UNIT_ADDRESS value 0.
3. Repeat step 2 using new, unique values for the DEVICE_UNIT_ADDRESS field in
HOST_CONF_REG_0 until all devices in the chain have been configured with their
own unique Unit Address value.
Note: t_{cmd_GSPI_conf} delay must be observed after every write that modifies
HOST_CONFIG_REG_0.
All connected devices receive this command (by default the Unit Address of all devices
is 0), and the Loop-Through operation will be re-established for all connected devices.
Once configured, each device will only respond to Command Words with a UNIT
ADDRESS field matching the DEVICE_UNIT_ADDRESS in HOST_CONF_REG_0
Note: Although the Loop-Through and Bus-Through configurations are compatible
with previous generation GSPI enabled devices (backward compatibility), only devices
supporting Unit Addressing can share a chip select. All devices on any single chip select
must be connected in a contiguous chain with only the last device's SDOUT connected
to the application host processor. Multiple chains configured in Bus-Through mode can
have their final SDOUT outputs connected to a single application host processor input.
GS3140
Final Data Sheet
PDS-060939
Rev.1
May 2015
www.semtech.com
29 of 40
Semtech
Proprietary & Confidential