GS4900B Datasheet, PDF (65/102 Pages) Semtech Corporation – SD Clock and Timing Generator with GENLOCK

3.10.1 Command Word Description
The command word consists of 16 bits transmitted MSB first and includes a read/write
bit, an Auto-Increment bit and a 12-bit address. Figure 3-12 shows the command word
format and bit configurations.
Command words are clocked into the GS4901B/GS4900B 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. This facilitates
multiple address writes without sending a command word for each data word.
Auto-Increment may be used for both read and write access.
MSB
LSB
R/W RSV RSV ^AutoInc A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0
RSV = Reserved. Must be set to zero. R/W: Read command when R/W = 1
Write command when R/W = 0
Figure 3-12: Command Word Format
MSB
LSB
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
Figure 3-13: Data Word Format
3.10.2 Data Read and Write Timing
Read and write mode timing for the GSPI interface is shown in Figure 3-14 and
Figure 3-15 respectively. The timing parameters are defined in Table 3-12.
When several devices are connected to the GSPI chain, only one CS should be asserted
during a read sequence.
During the write sequence, all command and following data words input at the SDIN pin
are output at the SDOUT pin as is. Where several devices are connected to the GSPI
chain, data can be written simultaneously to all the devices that have CS set LOW.
Table 3-12: GSPI Timing Parameters
Parameter
t₀
t₁
Definition
Specification
The minimum duration of time chip select, CS, must be
LOW before the first SCLK rising edge.
The minimum SCLK period.
1.5 ns
100 ns
GS4901B/GS4900B SD Clock and Timing Generator
with GENLOCK
Data Sheet
37703 - 4
December 2009
65 of 102