MC33661 Datasheet, PDF (14/20 Pages) Motorola, Inc – LIN Enhanced Physical Interface

Freescale Semiconductor, Inc.
OPERATIONAL MODES
Introduction
The 33661 has two communication modes, transmitting and
receiving modes, and two operational modes, normal and
sleep. The normal mode is differentiated by the slew rate—
normal, slow, or fast—of the LIN output.
Operational Modes
Normal Mode
In the normal mode, the 33661 has slew rate and timing
compatible with the LIN protocol specification and can operate
at 20 kbps. This mode is selected after sleep mode by setting
the TXD terminal HIGH prior to setting EN from LOW to HIGH.
Once normal mode is selected, it is impossible to select the
slow mode unless the 33661 is set to sleep mode.
Slow Mode
In the slow mode, the slew rate is around half the normal
slew rate, and bus speed operation is limited up to 10 kbps. The
radiated emission is significantly reduced compared to the
already excellent emission level of the normal mode. Slow
mode is entered after sleep mode by setting the TXD terminal
LOW prior to setting EN from LOW to HIGH. Once the slow
mode is selected, it is impossible to select the normal mode
unless the device is set to sleep mode.
Fast Mode
In the fast mode, the slew rate is around 10 times faster than
the normal mode. This allows very fast data transmission
(>100 kbps)—for instance, for ECU tests and microcontroller
program download. The bus pullup resistor might be reduced to
ensure a correct RC time constant in line with the high baud rate
used. Fast mode is entered via a special sequence (call toggle
function) at the TXD and EN terminals described in Figure 11
on page 11. Fast mode can be selected from either normal or
slow mode. Once in fast mode, the toggle function will bring the
device back in the previously selected mode (normal or slow).
A glitch on EN will also reset the device to the previously
selected mode (normal or slow) as shown in Figure 11 on
page 11.
Sleep Mode
In the sleep mode, the transmission path is disabled and the
33661 is in low power mode. Supply current from V_SUP is very
low. Wake-up can occur from LIN bus activity from node internal
wake-up through the EN terminal and from the WAKE input
terminal.
In the sleep mode, the 33661 has an internal 20 µA pullup
source to V_SUP. This avoids the high current path from the
battery to ground in the event the bus is shorted to ground.
(Refer to succeeding paragraphs describing wake-up
behavior.)
Device Wake-Up Events
The 33661 can be awakened from sleep mode by three
wake-up events: remote wake-up via LIN bus activity, internal
node wake-up via the EN terminal, or toggling the WAKE
terminal.
Remote Wake from LIN Bus
The LIN bus wake-up is recognized by a recessive-to-
dominant transition, followed by a dominant level with a
duration greater than 70 µs, followed by a dominant-to-
recessive transition. This is illustrated in Figures 7 and 10 on
page 10. Once the wake-up is detected, the 33661 enters the
“awake” mode, with INH HIGH and RXD pulled LOW.
Wake-Up from Internal Node Activity
The 33661 can wake up by internal node activity through a
LOW-to-HIGH transition of the EN terminal. When EN is
switched from LOW to HIGH, the device is awakened and
enters either the “normal” or the “wait slow” mode depending on
the level of TXD input. The MCU must set the TXD terminal
LOW or HIGH prior to waking up the device through the EN
terminal.
Wake-Up from WAKE Terminal
If the WAKE input terminal is toggled, the 33661 enters the
“awake” mode, with INH HIGH and RXD pulled LOW.
Device Power-Up
At power-up (V_SUP rises from zero), the 33661 automatically
switches in the “awake” mode. It switches the INH terminal to
HIGH state and RXD to LOW state. The MCU of the application
will then confirm normal or slow mode by setting the TXD and
EN terminals appropriately.
33661
14
MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA
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