WM2638
SOFTWARE CONFIGURATION OPTIONS
Production Data
The 16 bits of data can be transferred with the sequence shown in Table 2. D11-D0 contains the
12-bit data word. D15-D12 hold the programmable options which are summarized in Table 3.
D15 D14 D13 D12
R1 SPD PWD R0
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
New DAC value or control register value
D1
D0
Table 2 Serial Word Format
PROGRAMMABLE SETTLING TIME
Settling time is a software selectable 3.5µs or 1µs typical, to within
±0.5LSB
of final value. This is
controlled by the value of D14. A ONE defines a settling time of 1µs, a ZERO defines a settling time
of 3.5µs.
PROGRAMMABLE POWER DOWN
The power down function is controlled by D13. A ZERO configures the device as active, or fully
powered up, a ONE configures the device into power down mode. When the power down function is
released the device reverts back to the DAC code set prior to power down.
REGISTER ADDRESSING
A separate internal control register is available. This is accessed from the register access bits R1
(Bit D15) and R0 (Bit D12).
R1
(BIT D15)
0
0
1
1
R0
(BIT D12)
0
1
0
1
Write data to DAC B and BUFFER
Write data to BUFFER
Write data to DAC A and update DAC B with BUFFER content
Write data to control register
REGISTER
Table 3 Programmable Options
The contents of the control register, shown below in Table 3, are used to program the internal
reference function
D11
x
D10
x
D9
x
D8
x
D7
x
D6
x
D5
x
D4
x
D3
x
D2
X
D1
D0
REF1 REF0
Table 4 Control Register Contents
PROGRAMMABLE INTERNAL REFERENCE
The reference can be sourced internally or externally under software control. If an external reference
voltage is applied to the REF pin, the device must be configured to accept this.
If an external reference is selected, the reference voltage input is buffered which makes the DAC
input resistance independent of code. The REF pin has an input resistance of 10MΩ and an input
capacitance of typically 55pF. The reference voltage determines the DAC full-scale output.
If an internal reference is selected, a voltage of 1.024V or 2.048V is available. The internal
reference can source up to 1mA and can therefore be used as an external system reference.
REF1
(BIT D1)
0
0
1
1
REF0
(BIT D0)
0
1
0
1
External
1.024V
2.048V
External
REGISTER
Table 5 Internal Reference Options
WOLFSON MICROELECTRONICS LTD
PD Rev 1.0 July 99
8
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
