Freescale Semiconductor MC68HC908QT2 Header and Jumpers Blocks, Freescale Semiconductor, Inc

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

Operational Description

Header and Jumpers Blocks

2.4 Header and Jumpers Blocks

There is one 16-pin header (2 x 8-pin), J1, and four 2-pin jumper blocks,

JP1–JP4, on the PC board. See Figure 2-1for their locations on the PC board.

The header and jumper functions are described as follows.

J1:	Jumper block J1 is used to program the MC68HC908QT2, located in
	the center of the PC board. The connections to this board follow the
	standard MON08 connector scheme. It is also used to put the ASB520
	system into test mode. In a production environment, J1 could be
	replaced by a “bed of nails” test fixture to reduce PC board parts costs.
JP1:	Jumper block JP1 is on the PC board measure the current consumed
	by the microcontroller. Its primary purpose is to measure stop current of
	the microcontroller. A small trace on the bottom of the PC board must
	be cut to use this feature. When using this feature to measure stop
	current you should remove shorting jumper JP2. Removing the shunt
	from JP2 removes the system’s 470 ∝F bulk capacitor. Removing that
	capacitor will improve accuracy of the current measurement, as large
	capacitors have leakage current associated with them. Select the
	lowest voltage rating bulk capacitor for your circuit as possible because
	lower voltage rated ones tend to have less leakage than higher voltage
	ones for a given capacitance value.
JP2:	Jumper block JP2 disconnects the bulk capacitor during FLASH
	programming and optionally during stop current monitoring. The value
	of the capacitor is large enough to cause power switching issues when
	using the Cyclone programmer. During the programming procedure,
	the Cyclone programmer cycles power to the target PC board. Large
	value bulk capacitors greater than approximately 100 ∝F present
	excessive currents to the Cyclone programmer and interfere with the
	POR circuit of the target’s microcontroller as voltage on larger
	capacitance devices do not discharge fast enough during voltage
	cycling.
	The purpose for the bulk capacitor is two fold: First is tends to help lower
	the effects of the battery’s internal resistance during periods of high
	current demands while the IR LED is being modulated. This is a
	particular benefit toward the battery’s end of life period, when its internal
	resistance is increasing. Second, if a system uses RAM to store user
	information, the bulk capacitor will retain voltage to the microcontroller
	during battery changes.
JP3:	Jumper block JP3 disconnects pullup resistor, R9, during FLASH
	programming.
JP4:	Jumper block JP4 disconnects LED drive circuitry during FLASH
	programming.

Using the ASB520 MC68HC908QT2 Based Infrared Remote Control Reference PC Board		DRM045
MOTOROLA	Operational Description	13
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