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INTRODUCTION
WAN-0143
ADA and MASK Timing on WM9712
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.
WM9712 SETUP
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
REGISTER 4CH BIT 4 SETTING (PIN DEFINED AS INPUT OR OUTPUT) 1 (Input) 0 (Output) 1 or 0 (GPIO can be Input or Output)
Table 1 WM9712 Pin 47 Configuration
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
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.
11
Table 2 Controlling the MASK Feature
WOLFSON MICROELECTRONICS plc
March 2004, Rev 1.0.
Copyright 2004 Wolfson Microelectronics plc
www.wolfsonmicro.com
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
DEFAULT 0000 (1 frame) Delay Time
DESCRIPTION
Table 3 Delay Time Control (1)
DEL 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111
DELAY (AC-LINK FRAMES)
DELAY (TIME)
1 20.8s 2 41.7s 4 83.3s 8 167s 16 333s 32 667s 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.
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WAN_0143
INTERFACE TIMING
MASK
Frames (SYNC)
t DEL Conv t DEL t DEL t DEL Conv
AUXADC Conversion (MASK = 11)
AUXADC Conversion (MASK = 10)
Conv
Delay
Conv
Delay
Conv
Delay
Conv
Delay
AUXADC Conversion (MASK = 01)
Conv
Delay
Conv
Delay
Conv
Delay
Conv
Figure 1 MASK Delay Timings (tDEL = 2 frames)
PARAMETER Frame Delay set by register 76h
SYMBOL tDEL
MIN 0
TYP
MAX 288
UNIT frames
MASK
BCLK SYNC
t SETUP t HOLD tSETUP t HOLD
Figure 2 MASK Delay Timings
PARAMETER Setup time from MASK edge to SYNC 1 Hold time of MASK level from SYNC rising edge.
SYMBOL tSETUP tHOLD
MIN 162.8 81.4
TYP
MAX
UNIT ns ns
Note: 1. There must be at least two BCLK's between the rising edge of MASK and the rising edge of SYNC. Therefore, once MASK is high there must be at least two BCLK rising edges prior to the SYNC pulse.
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WAN_0143
ALTERNATIVE MASK FUNCTION
When MASK = 11, synchronous mode, conversions are commanded on the rising and falling edges of MASK input signal. However, there is an alternative operation which allows a pulse to be applied to the MASK pin resulting in only one conversion taking place. In this setup the edges of the pulse are too close together to allow two separate conversions to be commanded. Figure 3 details this operation and the timing associated.
t PULSE
MASK
Frames (SYNC)
t
DEL
t Conv
DEL
AUXADC Conversion (MASK = 11)
Conv
t
DEL
Figure 3 MASK PULSE delay timings (tDEL = 2 frames)
PARAMETER MASK Pulse Width Frame Delay set by register 76h
SYMBOL tPULSE tDEL
MIN 100ns 0
TYP
MAX < tDEL 288
UNIT ns frames
ADA TIMING
Whenever data becomes available from the touchpanel ADC, the internal ADA signal goes high and remains high until the data has been read from register 7Ah (if SLEN = 0) or until it has been sent out on an AC-Link slot (if SLEN = 1). If ADA is configured to be output on pin 47 the timing associated with this signal will be as follows.
BCLK
SYNC
ADA
t ADA t ADA
Figure 4 ADA Timings
PARAMETER Delay from SYNC to ADA
SYMBOL tADA
MIN
TYP 200ns
MAX
UNIT ns
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WAN_0143 SUMMARY
Pin 47 of the WM9712 has three possible functions which are: * * * MASK input, ADA output or General GPIO.
The modes and timings associated with MASK and ADA are detailed in this document. Further information on these functions and the GPIO operation is detailed in the WM9712 datasheet.
APPLICATION SUPPORT
If you require more information or require technical support please contact Wolfson Microelectronics Applications group through the following channels: Email: Telephone: Fax: Mail: apps@wolfsonmicro.com +44 (0)131 272 7070 +44 (0)131 272 7001 Applications at the address on last page.
or contact your local Wolfson representative. Additional information may be made available from time to time on our web site at http://www.wolfsonmicro.com
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WAN_0143 IMPORTANT NOTICE
Wolfson Microelectronics plc (WM) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current. All products are sold subject to the WM terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability.
WM warrants performance of its products to the specifications applicable at the time of sale in accordance with WM's standard warranty. Testing and other quality control techniques are utilised to the extent WM deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed, except those mandated by government requirements.
In order to minimise risks associated with customer applications, adequate design and operating safeguards must be used by the customer to minimise inherent or procedural hazards. Wolfson products are not authorised for use as critical components in life support devices or systems without the express written approval of an officer of the company. Life support devices or systems are devices or systems that are intended for surgical implant into the body, or support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided, can be reasonably expected to result in a significant injury to the user. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness.
WM assumes no liability for applications assistance or customer product design. WM does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right of WM covering or relating to any combination, machine, or process in which such products or services might be or are used. WM's publication of information regarding any third party's products or services does not constitute WM's approval, license, warranty or endorsement thereof.
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ADDRESS:
Wolfson Microelectronics plc Westfield House 26 Westfield Road Edinburgh EH11 2QW
Tel :: +44 (0)131 272 7000 Fax :: +44 (0)131 272 7001 Email :: apps@wolfsonmicro.com
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