CY24272
Document Number: 001-42414 Rev. **
Page 4 of 13
Device ID and SMBus Device Address
The device ID (ID0 and ID1) is a part of the SMBus device 8-bit
address. The least significant bit of the address designates a
write or read operation. Table 4 on page 3 shows the addresses
for four CY24272 devices on the same SMBus.
SMBus Protocol
The CY24272 is a slave receiver supporting operations in the
word and byte modes described in sections 5.5.4 and 5.5.5 of
the SMBus Specification 2.0.
DC specifications are modified to Rambus standard to support
1.8, 2.5, and 3.3 volt devices. Time out detection and packet
error protocol SMBus features are not supported.
Hold time for SDA is reduced relative to the CY24271, so that it
is compatible with I2C.
SMBus Data Byte Definitions
Three data bytes are defined for the CY24272. Byte 0 is for
programming the PLL multiplier registers and clock output
registers.
The definition of Byte 2 is shown in Table 6, Table 7, and Table 8
on page 5. The upper five bits are the revision numbers of the
device and the lower three bits are the ID numbers assigned to
the vendor by Rambus.
Notes
3. Bypass Mode: REFCLK bypasses the PLL to the output drivers.
4. Default mode of operation is at power up.
Table 5. Modes of Operation for CY24272
EN
/BYPASS RegTest RegA
RegB
RegC
RegD CLK0/CLK0B
CLK1/CLK1B
CLK2/CLK2B CLK3/CLK3B
L
X
X
X
X
X
X
High Z
High Z
High Z
High Z
H
X
1
X
X
X
X
Reserved for Vendor Test
H
L
0
X
X
X
X
REFCLK/
REFCLKB[3]
REFCLK/
REFCLKB
REFCLK/
REFCLKB
REFCLK/
REFCLKB
H
H
0
0
0
0
0
High Z
High Z
High Z
High Z
H
H
0
0
0
0
1
High Z
High Z
High Z
CLK/CLKB
H
H
0
0
0
1
0
High Z
High Z
CLK/CLKB
High Z
H
H
0
0
0
1
1
High Z
High Z
CLK/CLKB
CLK/CLKB
H
H
0
0
1
0
0
High Z
CLK/CLKB
High Z
High Z
H
H
0
0
1
0
1
High Z
CLK/CLKB
High Z
CLK/CLKB
H
H
0
0
1
1
0
High Z
CLK/CLKB
CLK/CLKB
High Z
H
H
0
0
1
1
1
High Z
CLK/CLKB
CLK/CLKB
CLK/CLKB
H
H
0
1
0
0
0
CLK/CLKB
High Z
High Z
High Z
H
H
0
1
0
0
1
CLK/CLKB
High Z
High Z
CLK/CLKB
H
H
0
1
0
1
0
CLK/CLKB
High Z
CLK/CLKB
High Z
H
H
0
1
0
1
1
CLK/CLKB
High Z
CLK/CLKB
CLK/CLKB
H
H
0
1
1
0
0
CLK/CLKB
CLK/CLKB
High Z
High Z
H
H
0
1
1
0
1
CLK/CLKB
CLK/CLKB
High Z
CLK/CLKB
H
H
0
1
1
1
0
CLK/CLKB
CLK/CLKB
CLK/CLKB
High Z
HH
0[4]
1[4]
1[4]
1[4]
1[4]
CLK/CLKB
CLK/CLKB
CLK/CLKB
CLK/CLKB
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