GS2972 Datasheet, PDF (88/125 Pages) Semtech Corporation – 3G/HD/SD-SDI Serializer with Complete SMPTE Audio & Video Support

4.13.1 Command Word Description
The Command Word consists of a 16-bit word transmitted MSB first and contains a
read/write bit, an Auto-Increment bit and a 12-bit address. Figure 4-30 shows the
command word format and bit configurations.
Command Words are clocked into the GS2972 on the rising edge of the Serial Clock
SCLK, which operates in a burst fashion.
When the Auto-Increment bit is set LOW, each Command Word must be followed by
only one Data Word to ensure proper operation. If the Auto-Increment bit is set HIGH,
the following Data Word will be written into the address specified in the Command
Word, and subsequent data words will be written into incremental addresses from the
previous Data Word. This facilitates multiple address writes without sending a
Command Word for each Data Word.
MSB
LSB
R/W RSV
RSV AutoInc A11 A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
Figure 4-30: Command Word Format
4.13.2 Data Read or Write Access
Serial data is transmitted or received MSB first synchronous with the rising edge of the
Serial Clock, SCLK. The Chip Select (CS) signal must be active LOW a minimum of
1.5ns (t0 in Figure 4-32) before the first clock edge to ensure proper operation.
During a Read sequence (Command Word R/W bit set HIGH), a wait state of
148ns (4 x 1/fPCLK, t5 in Figure 4-32) is required between writing the Command Word
and reading the following Data Word. The read bits are clocked out on the negative
edges of SCLK.
Note 1: Where several devices are connected to the GSPI chain, only one CS_TMS may
be asserted during a read sequence.
During a Write sequence (Command Word R/W bit set LOW), a wait state of
37ns (1 x 1/fPCLK, t4 in Figure 4-32) is required between the Command Word and the
following Data Word. This wait state must also be maintained between successive
Command Word/Data Word write sequences. When Auto-increment mode is selected
(AutoInc = 1), the wait state must be maintained between successive Data Words after
the initial Command Word/Data Word sequence.
During the write sequence, all command and following Data Words input at the SDIN
pin are output at the SDOUT pin as is.
When several devices are connected to the GSPI chain, data can be written
simultaneously to all the devices which have CS set LOW.
Note 2: If the application interface performs a Read or Write access after power-up,
prior to the application of a valid serial video input signal, the SCLK frequency must not
exceed 10MHz.
MSB
LSB
D15 D14 D13 D12 D11 D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
Figure 4-31: Data Word Format
GS2972 3G/HD/SD-SDI Serializer with Complete
SMPTE Audio & Video Support
Final Data Sheet Rev. 9
GENDOC-047479 September 2013
www.semtech.com
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