CMX994 Datasheet, PDF (24/61 Pages) CML Microcircuits – Local Oscillator

Direct Conversion Receivers
CMX994/CMX994A/CMX994E
7 C-BUS Interface and Register Descriptions
The C-BUS serial interface supports the transfer of data and control or status information between the
CMX994/CMX994A/CMX994E’s internal registers and an external host. Each C-BUS transaction consists of the
host sending a single Register Address byte, which may then be followed by zero or more data bytes that are
written into the corresponding CMX994/CMX994A/CMX994E register, as illustrated in Figure 16.
Data sent from the host on the Command Data (CDATA) line is clocked into the CMX994/CMX994A/CMX994E
on the rising edge of the Serial Clock (SCLK) input. The C-BUS interface is compatible with common µC/DSP
serial interfaces and may also be easily implemented with general purpose I/O pins controlled by a simple
software routine. Section gives the detailed C-BUS timing requirements.
Whether a C-BUS register is of the read or write type, it is fixed for a given C-BUS register address thus one
cannot both read and write the same C-BUS register address. The CMX994/CMX994A/CMX994E supports
several pairs of C-BUS register addresses in order to read and write the same information.
In order to provide ease of addressing when using this device with the CMX998 (Cartesian Feed-back Loop
Transmitter IC), the C-BUS addresses below are arranged so as not to overlap those used on the CMX998.
Thus, a common chip select (CSN) signal can be used, as well as common CDATA (SDI on CMX998), RDATA
(SDO on CMX998) and SCLK signals. Also note that the General Reset ($10) command on the
CMX994/CMX994A/CMX994E differs from other CML devices (such as CMX998), which use $01 for this
General Reset function. This allows the CMX994/CMX994A/CMX994E and CMX998 to be connected to the
same interface pins, including chip select, assuming the drive capabilities of the host are adequate.
C-BUS Write-only Registers
HEX
ADDRESS
REGISTER
$10
General Reset Register (Address only, no data)
$11
General Control Register, write only
$12
Rx Control Register, write only
$13
Rx Offset Register, write only
$14
LNA IM Control Register, write only
$15
Options Control Register, write only
$16
Rx Gain Register, write only
$17
Extended Rx Offset Register, write only
$20-$22 PLL M Divider Register, write only
$23-$24 PLL R Divider Register, write only
$25
VCO Control Register, write only
WORD SIZE
(BITS)
0
8
8
8
8
8
8
16
8
8
8
C-BUS Read-only Registers
HEX
ADDRESS
REGISTER
$E1
General Control Register, read only
$E2
Rx Control Register, read only
$E3
Rx Offset Register, read only
$E4
LNA IM Control Register, read only
$E5
Options Control Register, read only
$E6
Rx Gain Register, read only
$E7
Extended Rx Offset Register, read only
$D0-$D2 PLL M Divider Register, read only
$D3-$D4 PLL R Divider Register, read only
$D5
VCO Control Register, read only
WORD SIZE
(BITS)
8
8
8
8
8
8
16
8
8
8
CMX994A and CMX994E. Specific bits control CMX994E features only. See register descriptions for details.
CMX994A and CMX994E only
 2015 CML Microsystems Plc
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