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ADA and MASK Timing on WM9712



Wolfson Microelectronics plc 로고
Wolfson Microelectronics plc
WAN-0143 데이터시트, 핀배열, 회로
w
WAN-0143
ADA and MASK Timing on WM9712
INTRODUCTION
WM9712 SETUP
This applications note has been created to detail the timing of the MASK and ADA (ADC Data
Available) signals on the WM9712 device. This applications note should be used in conjunction with
the latest WM9712 datasheet.
The WM9712 has many additional functions to aid the design of portable applications. Pin 47 of the
device can be configured for either MASK input, ADA output or standard GPIO functionality. The
MASK function can be used to pause and control auxiliary ADC conversions. The ADA function can
be used to indicate when data becomes available from the auxiliary ADC. The timing associated
with both signals is detailed in the following sections of this document.
The WM9712 device must be configured to setup the function of pin 47. The three possible setups
are:
MASK Input Function
ADA Function
General GPIO
To set the device into one of the three above modes the following configurations should be used.
PIN 47 MODE
MASK
ADA
GPIO
REGISTER 56H BIT 4 SETTING
(GPIO FUNCTION SELECT)
1
1
0
Table 1 WM9712 Pin 47 Configuration
REGISTER 4CH BIT 4 SETTING
(PIN DEFINED AS INPUT OR OUTPUT)
1 (Input)
0 (Output)
1 or 0 (GPIO can be Input or Output)
MASK FUNCTION
Sources of glitch noise, such as the signals driving an LCD display, may feed through to the
touchscreen plates and affect measurement accuracy. In order to minimise this effect, a signal may
be applied to MASK (pin 47) to delay or synchronise the sampling of any input to the ADC. The effect
of the MASK signal depends on the MSK[1-0] bits of register 78h, as described below.
MSK[1-0]
00
01
10
11
EFFECT OF SIGNAL ON MASK PIN
MASK has no effect on conversions GPIO input disabled (default)
Static; ‘hi’ on MASK pin stops conversions, ‘lo’ has no effect.
Edge triggered; rising or falling edge on MASK pin delays conversions
by an amount set in the DEL[3-0] register. Conversions are asynchronous to
the MASK signal.
Synchronous mode; conversions wait until rising or falling edge on MASK
initiates cycle; screen starts to be driven when the edge arrives, the
conversion sample being taken a period set by DEL[3-0] after the edge.
Table 2 Controlling the MASK Feature
WOLFSON MICROELECTRONICS plc
www.wolfsonmicro.com
March 2004, Rev 1.0.
Copyright 2004 Wolfson Microelectronics plc


WAN-0143 데이터시트, 핀배열, 회로
WAN_0143
The delay described in Table 2 refers to the length of time delay there will be from the edge of the
MASK signal to the start of the next auxiliary ADC conversion. This delay is defined as shown in
Table 3 and Table 4 below.
REGISTER
ADDRESS
76h
BIT
7:4
LABEL
DEL
Table 3 Delay Time Control (1)
DEFAULT
DESCRIPTION
0000
(1 frame)
Delay Time
DEL
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
DELAY
DELAY
(AC-LINK FRAMES)
(TIME)
1 20.8µs
2 41.7µs
4 83.3µs
8 167µs
16 333µs
32 667µs
48 1ms
64 1.33ms
96 2ms
128 2.67ms
160 3.33ms
192 4ms
224 4.67ms
256 5.33ms
288 6ms
No delay, switch matrix always on
Table 4 Delay Time Control (2)
The delay associated to MASK is the same as the settling delay associated with the actual auxiliary
ADC measurement.
For example, when MODE is Edge triggered, an edge on the MASK input will cause the next auxiliary
ADC measurement to be delayed by the value set in register 76h. After this delay for MASK the
auxiliary ADC conversion will be started.
Figure 1 details the timing associated with the delay set to 2 frames for each of the active MASK
modes.
With MASK = 11, a conversion will be commanded and triggered by an edge of the MASK signal.
The delay from MASK edge to conversion is set by the DEL register setting. The delay is started on
the first SYNC pulse after an edge is detected on MASK (see figure 2 for further details).
With MASK = 10, a previously commanded conversion is paused by a delay reflected in the DEL
register setting.
With MASK = 01, any commanded conversions will be delayed while the MASK signal is HIGH.
Once the MASK signal returns low normal operation will resume.
w
Rev 1.0 March 2004
2




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ADA and MASK Timing on WM9712 - Wolfson Microelectronics plc