Texas Instruments MSP50C6xx - Manual (Page 358)

Initializing the MSP50C6xx
6-4
In any MSP50C614 application, it is important for certain components to be
located as close as possible to the MSP50C614 die or package. These include
any of the decoupling capacitors at V
DD
(0.1
µ
F). It also includes all of the
components in the crystal-reference network between OSC
IN
and OSC
OUT
(22 pF, 10 M
Ω
, 32 kHz).
6.2 Initializing the MSP50C6xx
The initialization code for the MSP50C6xx is in the file INIT.ASM, in the
MODULES\GENERAL directory of the TI-TALKS code (see the following
information).
The initialization routine does the following:
- Clears the status registers
- Clears all 32 accumulators
- Clears all 640 words of RAM
- Clears all system registers
- Sets the clock to run at 8.192 MHz. If CRO_FLAG is 1, the crystal oscillator
is used. Otherwise, If CRO_FLAG is 0, the resistor-trimmed oscillator is
used.
- Enables port F pullups
- Sets the DAC to 10 bits and turns it on
- Jumps to the label_main in MAIN.ASM
Note:
Care must be taken when branching to the init code to perform a software
reset on parts using resistor trim. The resistor trim is set based on the value
of fuses blown by the tester when the parts are manufactured. The P part
does not have these fuses so initially the value at that location is zero. If the
init routine encounters a zero it knows that it is running on a P part and sets
the resistor trim to a constant value, RESISTORTRIM. This will always work
properly after a hardware reset because all IO port locations are set to zero.
If the programmer branches to the init code to perform a software reset, the
value at 0x2F may not necessarily be zero. The IO addresses are not fully
decoded on the P part, so writing to 0x2C ( port G) also writes to 0x2D, 0x2E,
and 0x2F. This means that the value may not be zero during a software reset.
If this occurs, the init code will misidentify the P part as a C part and will use
the value at 0x2C as the trim. This may cause the P part to run at the wrong
speed. It is important to consider this if the init code is used as a software
reset. The C part has fuses at location 0x2C and fully decoded IO port ad-
dresses so this problem will not occur on masked parts.