CS4812
a buffer may be required to minimize the capacitive
loading on CLKOUT.
The 8-bit read instruction (00000011) is sent to the
EEPROM followed by a pre-defined 16-bit start ad-
dress.The CS4812 then automatically clocks out se-
quential bytes from the EEPROM until the last byte
has been received. After the last byte is received, the
CS4812 deasserts CS and begins program execution.
At this point, the serial control port becomes inactive
until the next reset.
CCLK and CS may be inputs or outputs with respect
to the CS4812. If the serial control port of the
CS4812 is defined as the master, then CCLK and CS
are outputs and CCLK requires a 2.2 kΩ pull-up re-
sistor. If the CS4812 is defined as the slave, then
CCLK and CS are inputs and no pull-up resistor is re-
quired on CCLK.
3.5.1.2 SPI Slave Mode
3.5.1.1 SPI Master Mode
In SPI slave mode, a write sequence from an exter-
nal host controller is shown in Figure 15. The host
controller asserts CS and sends a 16-bit write pre-
amble to the CS4812. This preamble consists of a
7-bit chip address (must be 0010000) followed by
a one-bit R/W (Read/Write) bit (set to 0 for write)
The SPI master mode is designed for read-only op-
eration during AutoBooting from a serial EE-
PROM. A typical AutoBoot sequence with a Xicor
X25650 serial EEPROM, or equivalent, is shown in
Figure 14. On exit from reset, the CS4812 asserts CS.
CS
0
1
2
3
4
5
6
7
8
9
10 11
21 22 23 24 25 26 27 28 29 30 31
CLK
DATA
DATA + n
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1 0
CDIN
READ
COMMAND
16-BIT
ADDRESS = 0X0000
0
0
0
0
0
0
1
1
0
0
0
0
0 0 0
CDOUT
MSB
Figure 14. Control Port Timing, SPI Master Mode AutoBoot
CS
(input)
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22
23
CLK
(input)
CHIP ADDRESS (WRITE)
MAP BYTE
DATA
DATA +n
INCR
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
0
0
1
0
0
0
0
0
7
6
5
4
3
2
1
0
CDIN
(input)
MSB
R/W
CDOUT
(output)
Figure 15. Control Port Timing, SPI Slave Mode Write
20
DS291PP3
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