AN3452| Application Note
Maxim/Dallas > App Notes > MICROCONTROLLERS Keywords: microcontrollers, 89C430, 89C450, 89C51, 89C51RD2, 87C520, 1-clock, UHSM
Jan 14, 2005
APPLICATION NOTE 3452
Instant Performance Enhancement with Flash Microcontrollers
Abstract: The ultra-high-speed flash microcontrollers (UHSFM) are 5V, 1-clock 8051s with integrated flash and SRAM. These UHSFMs drop into existing 8051 applications and deliver an instant boost in speed. This application note discusses the simple steps that may be required to port an existing 8051 application to the UHSFM family. The benefits of doing so are described.
Introduction
The ultra-high-speed microcontrollers (UHSM) are 5V, 1-clock 8051s with integrated flash and SRAM. These UHSMs drop into existing 8051 applications and, with little or no effort, give an instant boost in speed. In most cases UHSMs are 100% compatible with original 8051s, so no hardware or code changes are usually required. Three UHSMs are currently available: the DS89C430, DS89C440, and DS89C450, each with 16K, 32K, or 64K of flash memory, respectively. This article describes simple steps that may be required to port an original 8051 application to an UHSM. The benefits of using an UHSM are presented.
Architecture
As mentioned above, the UHSM is a single-clock-cycle 8051, instruction compatible with the original 8051 which relied on a 12-clock cycle architecture. Reducing the number of clocks per instruction to one enables up to 12 times better performance than the original 8051 at equivalent clock frequencies. Optionally, this also provides the ability to run at lower clock frequencies and yield the same performance while reducing overall system power consumption. For greater performance and noise reduction, the UHSM also integrates a clock multiplier that allows either two or four times multiplication of the external crystal. The UHSM, for example, could be used in an existing 7.372MHz 8051 design and run clock quadrupled 29.49 MHz internally. Not only does the on-board clock rate of 29.49MHz improve performance, but by keeping this high frequency isolated internally on the microcontroller, external noise is also kept to a minimum. This greatly reduces EMI. The UHSMs contain several additional features that make the
m an excellent choice for new designs:
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Dual datapointers with automatic increment/decrement and toggle select In-application programmable Flash 1K byte SRAM for MOVX Power Management Modes: Idle Mode, Stop Mode, Divide-by-1024 Mode Two serial ports Watchdog timer Power-fail reset and early warning power-fail interrupt
Compatibility
Code The UHSM is 8051-instruction compatible, and in most cases no changes to the code are required. Code-based timing loops, however, must be rewritten and recalculated against the single-cycle instruction timings. To take further advantage of the performance enhancements of the UHSMs, a few other small code changes are required. One example is using the divide-by-4 option on the timers to allow higher baud rates. Another example is using the datapointer auto inc/dec options to speed up copy, clear, and compare operations.
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