w WAN-0143 ADA and MASK Timing on WM9712 INTRODUCTION 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 REGISTER 56H BIT 4 SETTING (GPIO FUNCTION SELECT) REGISTER 4CH BIT 4 SETTING (PIN DEFINED AS INPUT OR OUTPUT) MASK 1 1 (Input) ADA 1 0 (Output) GPIO 0 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] EFFECT OF SIGNAL ON MASK PIN 00 MASK has no effect on conversions GPIO input disabled (default) 01 Static; ‘hi’ on MASK pin stops conversions, ‘lo’ has no effect. 10 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. 11 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 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) DESCRIPTION Delay Time 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 20.8µs 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 WAN_0143 INTERFACE TIMING MASK Frames (SYNC) t DEL AUXADC Conversion (MASK = 11) t DEL Conv Conv t DEL t DEL AUXADC Conversion (MASK = 10) Conv AUXADC Conversion (MASK = 01) Conv Delay Conv Delay Delay Delay Conv Delay Conv Conv Conv Delay Delay Conv Figure 1 MASK Delay Timings (tDEL = 2 frames) PARAMETER SYMBOL Frame Delay set by register 76h tDEL MIN TYP 0 MAX UNIT 288 frames MASK BCLK SYNC t SETUP t HOLD tSETUP t HOLD Figure 2 MASK Delay Timings PARAMETER SYMBOL MIN Setup time from MASK edge to SYNC 1 tSETUP 162.8 TYP MAX UNIT ns Hold time of MASK level from SYNC rising edge. tHOLD 81.4 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. w Rev 1.0 March 2004 3 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 AUXADC Conversion (MASK = 11) t DEL DEL Conv t Conv DEL Figure 3 MASK PULSE delay timings (tDEL = 2 frames) PARAMETER MASK Pulse Width Frame Delay set by register 76h SYMBOL MIN tPULSE 100ns tDEL TYP MAX < tDEL 0 288 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 w SYMBOL tADA MIN TYP 200ns MAX UNIT ns Rev 1.0 March 2004 4 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: [email protected] +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 w Rev 1.0 March 2004 5 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. 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