DESIGNCYCLETHE
ADVANCED TECHNIQUES FOR DESIGN ENGINEERS
■ BY FRED EADY
Still Rockin’ the microSD Card
It took a while, but paper punch cards finally bit the dust. Good old RS-232
is in the rocking chair, as well. These days, thanks to the microcontroller
industries’ hardware refinements and ready-to-run library code, putting a
USB portal online is just as easy as building an RS-232 interface.
The very first embedded computing devices wielded four bits. After the
dust settled, eight-bit devices proved superior. Despite the emergence of
multifaceted 16- and 32-bit microcontrollers, eight-bit microcontrollers are
still a viable and powerful embedded control platform. If you had time to join
us last month, you’ll recall that we took a look at an eight-bit microcontroller
capable of communicating with SPI, I2C, RS-232, and USB capable external
devices. That particular eight-bit microcontroller used the SPI protocol to
enhance its data storage capability via a microSD card.
EIGHT BITS IS STILL A BYTE
Eight-bit microcontrollers still pack a punch. The
PIC18F46J50 we discussed last month is a very capable
eight-bit embedded computing platform. However, with
the Microchip bootloader code falling into a little less than
half of the PIC18F46J50’s program Flash, any bootloader
application based on this PIC will have to reside within
34K or less of program Flash.
Many of the past Design Cycle projects have been
based on the PIC18LF4620 and its relatives. The
PIC18F46J50 just happens to be a USB-enabled
PIC18LF4620 with peripheral pin select. This
microcontroller we will walk around here is yet another
enhanced version of the PIC18LF4620.
The PIC18F47J53 is well suited for use with the
microSD card in a bootloader application. With the
bootloader application loaded in program Flash, the
PIC18F47J53 can still offer about 98K of
program Flash for the user’s application. If
power conservation is a factor, the
PIC18F47J53 can fall into a deep sleep while
maintaining the correct time via its on-chip real
time clock calendar subsystem. The
PIC18F47J53 is a 3. 3 volt part that is designed
to easily interface to external 5.0 volt
peripherals. All of the PIC18F47J53 I/O pins
that are associated with communication
protocols are 5.0 volt tolerant. The
PIC18F47J53’s parallel master port pins are also
5.0 volt tolerant. Basically, the PIC18F47J53 is a
■ PHOTO 1. The USCM-47J53 is a resource-enhanced USCM-46J50 that is intended to be
placed in microSD card applications that need
more program Flash. The USCM-47J53 also
sports a 3. 3 volt EA DOGM162L-A LCD module
and a MOSFET power switch.
54
December 2010