LMH0394_15 Datasheet, PDF (15/35 Pages) Texas Instruments – 3G HD/SD SDI Low Power Extended Reach Adaptive Cable Equalizer

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Programming (continued)
LMH0394
SNLS312M – AUGUST 2010 – REVISED JULY 2015
MISO
Host
MOSI
Device 1
LMH0394
MOSI MISO
Device 2
LMH0394
MOSI MISO
Device 3
LMH0394
MOSI MISO
Device N
LMH0394
MOSI MISO
SCK
SS
Figure 10. SPI Daisy Chain System Architecture
In a daisy-chain configuration of N LMH0394 devices, the host conceptually sees a shift register of length 16xN.
Therefore the length of SPI transactions (as previously described) is 16xN bits, and SS must be asserted for
16xN clock cycles for each SPI transaction.
7.5.1.5 SPI Daisy-Chain Write
Figure 11 shows the SPI daisy-chain write for a daisy-chain of N devices. The SS signal is driven low and SCK is
toggled for 16xN clocks. The 16xN bit MOSI payload (sent to Device 1 in the daisy-chain) consists of the 16-bit
SPI write data for Device N (the last device in the chain), followed by the write data for Device –1, Device –2,
etc., ending with the write data for Device 1 (the first device in the chain). The 16-bit SPI write data for each
device consists of a “0” (write command), seven address bits, and eight data bits. After the SPI daisy-chain write,
SS must return high and then the write occurs for all devices in the daisy-chain.
SPI Write Data
0 A6 A5 A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0
SS
(host)
SCK
(host)
MOSI (host)
MOSI Device 1
Device N
Write Data
Device N-1
Write Data
MISO Device 1
MOSI Device 2
'21¶7&$5(
Device N
Write Data
16xN clocks
Device N-2
Write Data
Device N-3
Write Data
Device N-1
Write Data
Device N-2
Write Data
Device 1
Write Data
Device 2
Write Data
MISO Device N-1
MOSI Device N
'21¶7&$5(
'21¶7&$5(
'21¶7&$5(
'21¶7&$5(
Figure 11. SPI Daisy-Chain Write
Device N
Write Data
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