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uM-FPU V1.0

Pin Descriptions
Note: The following page contains documentation and support software for uM-FPU V1.0, the original version of the uM-FPU floating point coprocessor.

See uM-FPU V2 or uM-FPU V3 for details on newer versions.


The uM-FPU V1.0 floating point coprocessor is easily interfaced with most microcontrollers to provide support for 32-bit IEEE 754 compatible floating point and long integer operations. The microcontroller communicates with the uM-FPU using a 2-wire or 3-wire SPI compatible interface. The 8-pin uM-FPU uses an internal oscillator and requires no external components.


uM-FPU V1.0 Datasheet
248 KB PDF Oct 30, 2004
uM-FPU V1.0 Instruction Timing 116 KB PDF Sep 8, 2004
uM-FPU V1.0 BASIC Reference 260 KB PDF Apr 29, 2004
uM-FPU V1.0 Javelin Reference 192 KB PDF Apr 27, 2004
uM-FPU PICAXE V1.0 Reference 188 KB PDF Jul 7, 2004
uM-FPU V1.0 PICmicro Reference 200 KB PDF Oct 18, 2004
uM-FPU V1.0 IDE Reference 252 KB PDF Aug 11, 2004


BASIC Stamp Software for uM-FPU V1.0 20 KB ZIP May 22, 2004
Javelin Stamp Software for uM-FPU V1.0 24 KB ZIP May 22, 2004
PICmicro Software for uM-FPU V1.0 105 KB ZIP Oct 18, 2004
PICAXE Software for uM-FPU V1.0 12 KB ZIP May 22, 2004
PicBasic Pro Software for uM-FPU V1.0 16 KB ZIP Jan 21, 2005
uM-FPU V1.0 IDE (beta) 1 MB ZIP May 22, 2004
uM-FPU Converter (with uM-FPU V1.0 samples) 712 KB ZIP May 22, 2004

Pin Descriptions

 Pin   Name  Type  Description
1  SOUT  Output   SPI Output
2  SIN  Input  SPI Input
3  /CS  Input  Chip Select
4  VSS  Power  Ground
5  TSTOUT   Output  Test Output
6  TSTIN  Input  Test Input
7  SCLK  Input  SPI Clock
8  VDD  Power  Supply Voltage 

uM-FPU V1 - Known Problems

When the FTOA instruction is used for formatted output, the minus sign is sometimes not displayed properly.

This problem only occurs with formatted floating point conversions, unformatted conversions (format = 0) are not affected.

When the FTOA instruction is used for formatted output, an internal variable is set incorrectly. If the value being converted is negative, the sign is displayed properly, but if the value is positive, an internal sign variable is not set and the value will depend on the last operation that set this variable. The following workaround will fix the problem for the BASIC Stamp.

At the beginning of the Print_FloatFormat routine insert the following code:

  fLow.HIGHNIB = fA
  fA = 0
  GOSUB Fabs
  GOSUB Fabs
  fA = fLow.HIGHNIB

The two FABS instructions ensure that the internal variable is cleared before the FTOA instruction.

A similar workaround can be used for other microcontrollers.

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