LMH0318_15 Datasheet, PDF (23/57 Pages) Texas Instruments – LMH0318 3 Gbps HD/SD SDI Reclocker with Integrated Cable Driver

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LMH0318
SNLS508 – SEPTEMBER 2015
8.3.7.8 SPI Daisy Chain
The LMH0318 includes an enhanced SPI controller that supports daisy-chaining the serial configuration data
among multiple LMH0318 devices. The LMH0318 device supports SPI Daisy Chain between devices with an 8-
bit SPI addressing scheme. Each LMH0318 device is directly connected to the SCK and SS_N pins of the Host.
However, only the first LMH0318 device in the chain is connected to the Host’s MOSI pin, and only the last
device in the chain is connected to the Host’s MISO pin. The MOSI pin of each intermediate LMH0318 device in
the chain is connected to the MISO pin of the previous LMH0318 device, thereby creating a serial shift register.
This architecture is shown in Figure 12.
MISO
Host
MOSI
Device 1
LMH0318
MOSI MISO
Device 2
LMH0318
MOSI MISO
Device 3
LMH0318
MOSI MISO
...
Device N
LMH0318
MOSI MISO
SCK
SS
Figure 12. Daisy-Chain Configuration
In a daisy-chain configuration of N LMH0318 devices, the Host conceptually sees a long shift register of length
17xN. Therefore the length of a Basic SPI Transaction, as described above, is 17xN; in other words, SS_N is
asserted for 17xN clock cycles.
8.3.7.8.1 SPI Daisy Chain Write Example
The following example make some assumptions:
The daisy-chain is 3 LMH0318 devices long, comprising Devices 1, 2, and 3 as shown in Figure 12. Therefore,
each Basic SPI Transaction is 17x3 = 51 clocks long.
In Figure 13, the following occurs at the end of the transaction:
• Write 0x5A to register 0x12 in Device 3
• Write 0x3C to register 0x34 in Device 2
• Write 0x00 to register 0x56 in Device 1
Note that the bits are shifted out of MOSI left to right. The MISO pin is not shown as it reflects shift register
contents from a prior transaction.
MOSI
(Write)
0 0x12 0x5A 0 0x34 0x3C 0 0x56 0x00
Figure 13. MOSI Write Example
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