33813 Datasheet, PDF (27/54 Pages) Freescale Semiconductor, Inc – One Cylinder Small Engine Control IC

5.1.15 ISO9141 Transceiver (MTX, MRX, ISO9141)
These three pins are used to provide an ISO914, K-line communication link for the MCU to provide diagnostic support TACHOUT
OUTPUT for the system. MRX is the 5.0 V logic level serial output line to the MCU. MTX is the 5.0 V logic level serial input to the
IC from the MCU. The ISO9141 pin is a bi-directional line, consistent with the ISO9141 specification for signalling to and from
the MCU. There is only one bit in the SPI Status register to indicate an over-temperature fault from the ISO9141 functional block.
There are no Configuration or Control registers associated with this functional block.
5.1.16 Tachometer (TACHOUT)
The TACHOUT pin is a low side driver, that can used to drive a tachometer meter movement. TACHOUT can be programmed
via the SPI to:
1. Output the same signal as VRSOUT divided by a 1 to 32 programmable divider,
2. Output a PWM signal with a frequency and duty cycle programmable via the SPI, or
3. Output one of 8 fixed frequencies as indicated in Table 6.
If a tachometer is not required the TACHOUT output can also be used as a low current, SPI controlled, low side driver to drive a
LED or other low current load. The SPI Configuration register for the Tachometer is used to determine which mode this output
will be used in. The TACHOUT output handles over-current (OC) differently than the other low side drivers. When an over-current
limit is reached the TACHOUT output does not enter a current limiting state but rather shuts the output off to protect the output
device. The retry option works similarly to the other low side drivers.
In the LSD mode bit 4 of the SPI Configuration register controls the turn on or turn off of the Open Load detect current sink.
Table 6. TACHOUT SPI Configuration Register
SPI Configuration Register 4 Bits 6, 5
00 (default)
01
10
11
TACHOUT Mode
VRSOUT divided by ‘N’
where ‘N’ is defined by bits 0 thru 4 of SPI Configuration Register 4 (1 - 32)
00001 = 1 (default)
.
11111 = 31
00000=32
Oscillator Output
Low Side Driver (LSD)
Same as 10 above
Table 7. TACHOUT SPI Configuration Register
SPI Configuration Register Bits 2,1,0
000 (default)
001
010
011
100
101
110
111
Oscillator Frequencies
10 Hz
100 Hz
1.0 kHz
5.0 kHz
10 kHz
20 kHz
40 kHz
100 kHz (not recommended for use)
Analog Integrated Circuit Device Data
Freescale Semiconductor
33813
27