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WM9712L Datasheet(PDF) 46 Page - Wolfson Microelectronics plc |
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WM9712L Datasheet(HTML) 46 Page - Wolfson Microelectronics plc |
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46 / 77 page  WM9712L Production Data w PD Rev 4.5 August 2006 46 Setting DEL to ‘1111’ reduces the settling time to zero, i.e. measurements begin immediately. This mode is intended for fast sampling on AUX inputs. It is NOT intended for touchpanel digitisation. There are several side-effects when DEL is set to ‘1111’: • Co-ordinate mode does not work, i.e. the WM9712L behaves as if COO = 0, even if COO = 1 (see “Measurement Types”) • If X / Y co-ordinate or touch pressure measurements are selected (ADCSEL = 001, 010 or 011), then the switch matrix is constantly on, and current constantly flows in the touchpanel. This increases power consumption in the system, and is therefore not recommended for battery powered systems • In continuous mode (CTC = 1), setting DEL = 1111 increases the sampling rate of the touchpanel ADC (see “Initiation of Measurements”) MASK INPUT CONTROL 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 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 33 Controlling the MASK Feature Note that pin 47 can also be used as a GPIO(see “GPIO and Interrupt Control” section), or to output the ADA signal (see below). THE ADA SIGNAL Whenever data becomes available from the touchpanel ADC, the internal ADA (ADC Data Available) 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). ADA can be used to generate an interrupt, if the AW bit (register 52h, bit 12) is set (see “GPIO and interrupt control” section) It is also possible to output the ADA signal on pin 47, if this pin is not used as a GPIO. The GE4 bit (register 56h, bit 12) must be set to ‘0’ to achieve this (see “GPIO and interrupt control” section). Alternatively, ADA can be read from bit 12 in register 54h. |
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