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AFE4490 Datasheet(PDF) 26 Page - Texas Instruments |
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AFE4490 Datasheet(HTML) 26 Page - Texas Instruments |
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26 / 69 page  AFE4400 SBAS601D – DECEMBER 2012 – REVISED MAY 2013 www.ti.com Using the Timer Module The timer module registers can be used to program the start and end instants in units of 4-MHz clock cycles. These timing instants and the corresponding registers are listed in Table 2. Note that the device does not restrict the values in these registers; thus, the start and end edges can be positioned anywhere within the pulse repetition period. Care must be taken by the user to program suitable values in these registers to avoid overlapping the signals and to make sure none of the edges exceed the value programmed in the PRP register. Writing the same value in the start and end registers results in a pulse duration of one clock cycle. The following steps describe the timer sequencing configuration: 1. With respect to the start of the PRP period (indicated by timing instant t0 in Figure 41), the following sequence of conversions must be followed in order: convert LED2 → LED2 ambient → LED1 → LED1 ambient. 2. Also, starting from t0, the sequence of sampling instants must be staggered with respect to the respective conversions as follows: sample LED2 ambient → LED1 → LED1 ambient → LED2. 3. Finally, align the edges for the two LED pulses with the respective sampling instants. Table 2. Clock Edge Mapping to SPI Registers TIME INSTANT (See Figure 41 and EXAMPLE Figure 42) DESCRIPTION CORRESPONDING REGISTER ADDRESS AND REGISTER BITS (Decimal) t0 Start of pulse repetition period No register control — t1 Start of sample LED2 pulse LED2STC[15:0], register 01h 4800 t2 End of sample LED2 pulse LED2ENDC[15:0], register 02h 6399 t3 Start of LED2 pulse LED2LEDSTC[15:0], register 03h 4800 t4 End of LED2 pulse LED2LEDENDC[15:0], register 04h 6399 t5 Start of sample LED2 ambient pulse ALED2STC[15:0], register 05h 0 t6 End of sample LED2 ambient pulse ALED2ENDC[15:0], register 06h 1599 t7 Start of sample LED1 pulse LED1STC[15:0], register 07h 1600 t8 End of sample LED1 pulse LED1ENDC[15:0], register 08h 3199 t9 Start of LED1 pulse LED1LEDSTC[15:0], register 09h 1600 t10 End of LED1 pulse LED1LEDENDC[15:0], register 0Ah 3199 t11 Start of sample LED1 ambient pulse ALED1STC[15:0], register 0Bh 3200 t12 End of sample LED1 ambient pulse ALED1ENDC[15:0], register 0Ch 4799 t13 Start of convert LED2 pulse LED2CONVST[15:0], register 0Dh 2 LED2CONVEND[15:0], register 0Eh t14 End of convert LED2 pulse 1599 Must start one AFE clock cycle after the ADC reset pulse ends. ALED2CONVST[15:0], register 0Fh t15 Start of convert LED2 ambient pulse 1602 Must start one AFE clock cycle after the ADC reset pulse ends. t16 End of convert LED2 ambient pulse ALED2CONVEND[15:0], register 10h 3199 LED1CONVST[15:0], register 11h t17 Start of convert LED1 pulse 3202 Must start one AFE clock cycle after the ADC reset pulse ends. t18 End of convert LED1 pulse LED1CONVEND[15:0], register 12h 4799 ALED1CONVST[15:0], register 13h t19 Start of convert LED1 ambient pulse 4802 Must start one AFE clock cycle after the ADC reset pulse ends. t20 End of convert LED1 ambient pulse ALED1CONVEND[15:0], register 14h 6399 t21 Start of first ADC conversion reset pulse ADCRSTCNT0[15:0], register 15h 0 t22 End of first ADC conversion reset pulse ADCRSTENDCT0[15:0], register 16h 0 t23 Start of second ADC conversion reset pulse ADCRSTSTCT1[15:0], register 17h 1600 t24 End of second ADC conversion reset pulse ADCRSTENDCT1[15:0], register 18h 1600 t25 Start of third ADC conversion reset pulse ADCRSTSTCT2[15:0], register 19h 3200 t26 End of third ADC conversion reset pulse ADCRSTENDCT2[15:0], register 1Ah 3200 t27 Start of fourth ADC conversion reset pulse ADCRSTSTCT3[15:0], register 1Bh 4800 t28 End of fourth ADC conversion reset pulse ADCRSTENDCT3[15:0], register 1Ch 4800 t29 End of pulse repetition period PRPCOUNT[15:0], register 1Dh 6399 26 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: AFE4400 |
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