AFE4490 datasheet(24/70 Pages) TI

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AFE4490

SBAS602B – DECEMBER 2012 – REVISED FEBRUARY 2013

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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 35), the 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 35 and

EXAMPLE

Figure 36)

DESCRIPTION

CORRESPONDING REGISTER ADDRESS AND REGISTER BITS

(Decimal)

Start of pulse repetition period

No register control

—

Start of sample LED2 pulse

Sample LED2 start count (bits 15-0 of register 01h)

4800

End of sample LED2 pulse

Sample LED2 end count (bits 15-0 of register 02h)

6399

Start of LED2 pulse

LED2 start count (bits 15-0 of register 03h)

4800

End of LED2 pulse

LED2 end count (bits 15-0 of register 04h)

6399

Start of sample LED2 ambient pulse

Sample ambient LED2 start count (bits 15-0 of register 05h)

End of sample LED2 ambient pulse

Sample ambient LED2 end count (bits 15-0 of register 06h)

1599

Start of sample LED1 pulse

Sample LED1 start count (bits 15-0 of register 07h)

1600

End of sample LED1 pulse

Sample LED1 end count (bits 15-0 of register 08h)

3199

Start of LED1 pulse

LED1 start count (bits 15-0 of register 09h)

1600

t10

End of LED1 pulse

LED1 end count (bits 15-0 of register 0Ah)

3199

t11

Start of sample LED1 ambient pulse

Sample ambient LED1 start count (bits 15-0 of register 0Bh)

3200

t12

End of sample LED1 ambient pulse

Sample ambient LED1 end count (bits 15-0 of register 0Ch)

4700

t13

Start of convert LED2 pulse

LED2 convert start count (bits 15-0 of register 0Dh)

t14

End of convert LED2 pulse

LED2 convert end count (bits 15-0 of register 0Eh)

1599

t15

Start of convert LED2 ambient pulse

LED2 ambient convert start count (bits 15-0 of register 0Fh)

1600

t16

End of convert LED2 ambient pulse

LED2 ambient convert end count (bits 15-0 of register 10h)

3199

t17

Start of convert LED1 pulse

LED1 convert start count (bits 15-0 of register 11h)

3200

t18

End of convert LED1 pulse

LED1 convert end count (bits 15-0 of register 12h)

4799

t19

Start of convert LED1 ambient pulse

LED1 ambient convert start count (bits 15-0 of register 13h)

4800

t20

End of convert LED1 ambient pulse

LED1 ambient convert end count (bits 15-0 of register 14h)

6399

t21

Start of first ADC conversion reset pulse

ADC reset 0 start count (bits 15-0 of register 15h)

t22

End of first ADC conversion reset pulse

ADC reset 0 end count (bits 15-0 of register 16h)

t23

Start of second ADC conversion reset pulse

ADC reset 1 start count (bits 15-0 of register 17h)

1600

t24

End of second ADC conversion reset pulse

ADC reset 0 end count (bits 15-0 of register 18h)

1600

t25

Start of third ADC conversion reset pulse

ADC reset 2 start count (bits 15-0 of register 19h)

3200

t26

End of third ADC conversion reset pulse

ADC reset 0 end count (bits 15-0 of register 1Ah)

3200

t27

Start of fourth ADC conversion reset pulse

ADC reset 3 start count (bits 15-0 of register 1Bh)

4800

t28

End of fourth ADC conversion reset pulse

ADC reset 0 end count (bits 15-0 of register 1Ch)

4800

t29

End of pulse repetition period

Pulse repetition period count (bits 15-0 of register 1Dh)

6399

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