CS5530
DS742F3
17
2.2.4 Reading/Writing On-Chip Registers
The CS5530’s offset, gain, and configuration regis-
ters are readable and writable while the conversion
data register is read only.
As shown in Figure 7, to write to a particular regis-
ter the user must transmit the appropriate write
command and then follow that command by 32 bits
of data. For example, to write 0x80000000 (hexa-
decimal) to the gain register, the user would first
transmit the command byte 0x02 (hexadecimal)
followed by the data 0x80000000 (hexadecimal).
Similarly, to read a particular register the user must
transmit the appropriate read command and then
acquire the 32 bits of data. Once a register is written
to or read from, the serial port returns to the com-
mand mode.
2.3 Configuration Register
To ease the architectural design and simplify the
serial interface, the configuration register is thirty-
two bits long, however, only fifteen of the thirty
two bits are used. The following sections detail the
bits in the configuration register.
2.3.1 Power Consumption
The CS5530 accommodates three power consump-
tion modes: normal, standby, and sleep. The default
mode, “normal mode”, is entered after power is ap-
plied. In this mode, the CS5530 typically consumes
35 mW. The other two modes are referred to as the
power save modes. They power down most of the
analog portion of the chip and stop filter convolu-
tions. The power save modes are entered whenever
the power down (PDW) bit of the configuration
register is set to logic 1. The particular power save
mode entered depends on state of the PSS (Power
Save Select) bit. If PSS is logic 0, the converter en-
ters the standby mode reducing the power con-
sumption to 4 mW. The standby mode leaves the
oscillator and the on-chip bias generator for the an-
alog portion of the chip active. This allows the con-
verter to quickly return to the normal mode once
PDW is set back to a logic 0. If PSS and PDW are
both set to logic 1, the sleep mode is entered reduc-
ing the consumed power to around 500
μ
W. Since
this sleep mode disables the oscillator, approxi-
mately a 20 ms oscillator start-up delay period is
required before returning to the normal mode. If an
external clock is used, there will be no delay.
2.3.2 System Reset Sequence
The reset system (RS) bit permits the user to per-
form a system reset. A system reset can be initiated
at any time by writing a logic 1 to the RS bit in the
configuration register. After the RS bit has been
set, the internal logic of the chip will be initialized
to a reset state. The reset valid (RV) bit is set indi-
cating that the internal logic was properly reset.
The RV bit is cleared after the configuration regis-
ter is read. The on-chip registers are initialized to
the following default states:
After reset, the RS bit should be written back to
logic 0 to complete the reset cycle. The ADC will
return to the command mode where it waits for a
valid command. Also, the RS bit is the only bit in
the configuration register that can be set when ini-
tiating a reset (i.e. a second write command is need-
ed to set other bits in the Configuration Register
after the RS bit has been cleared).
2.3.3 Input Short
The input short bit allows the user to internally
ground the inputs of the ADC. This is a useful func-
tion because it allows the user to easily test the
grounded input performance of the ADC and elim-
inate the noise effects due to the external system
components.
2.3.4 Voltage Reference Select
The voltage reference select (VRS) bit selects the
size of the sampling capacitor used to sample the
voltage reference. The bit should be set based upon
Configuration Register:
00000000(H)
Offset Register:
00000000(H)
Gain Register
01000000(H)
