Nuts and Volts - December 2010

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.