MC68HC58 Motorola, MC68HC58 Datasheet - Page 29

• Manufacturer Part Number: MC68HC58
• Description: Data Link Controller
• Manufacturer: Motorola

2.5 Power Supply Connections
MC68HC58
TECHNICAL DATA
During standby mode, the DLC oscillator and most internal circuitry are inactive. Pow-
er consumption is reduced significantly.
The host MCU must send the DLC a command byte to initiate low power operation,
but the DLC can be reactivated in a number of ways. A DLC can come out of standby
when it detects J1850 bus activity, when its status register is read by the host MCU,
or when power is applied. If interrupts are enabled, the DLC can issue an interrupt re-
quest to the host MCU when it is activated.
The way in which power is applied to the DLC affects activation out of standby mode.
Ignition switch position, battery drain during engine cranking, and alternator power sta-
bility can affect the supplies available at the time J1850 bus activity brings the DLC out
of standby mode.
There are three recommended methods of implementing operation. Methods 1 and 2
permit the receiver to be activated by a frame on the J1850 bus. With a 4 or 8 MHz
resonator, a properly configured DLC can accurately receive the frame that activates
it. If interrupts are enabled, methods 1 and 3 permit the DLC to generate an interrupt
request upon activation. Method 2 does not permit the DLC to generate an interrupt
request when it is activated, because the control logic is not powered when J1850 bus
activity is detected. Refer to SECTION 4 DATA LINK CONTROLLER OPERATION
for more information on DLC interrupt service requests.
SIGNAL AND PIN DESCRIPTIONS
MOTOROLA
2-13