AN1229
DS01229C-page 12 2008-2012 Microchip Technology Inc.
Addressing of Variable and Invariable
Memory and Internal Data Path
For single chip microcontrollers or digital signal
controllers, such as PIC MCUs and dsPIC DSCs, the
Periodic Static Memory test is used to test the variable
memory, and the periodic checksum is used to test the
invariable memory. These tests detect any stuck-at
Fault in the internal address bus and internal data path.
Addressing Wrong Address
This test is required only for microcontrollers with an
external memory device.
External Communication
The IEC 60730 Class B specifications suggest the
following measures to ensure reliable communication
between components:
TRANSFER REDUNDANCY
The transfer redundancy is a Fault/error control
technique that protects against coincidental and/or
systematic errors in the input and output information. It
is achieved by transferring the data between the trans-
mitter and receiver. The data is transferred at least
twice in succession and then compared.
PROTOCOL TEST
The Protocol test is a Fault/error control technique in
which the data is transferred to and from the computer
components to detect errors in the internal
communication protocol.
CRC SINGLE WORD
A CRC polynomial is used to calculate the CRC check-
sum of the transmitted message. At the transmitting
end, this CRC checksum is appended to the message
before transmitting it. At the receiving end, the receiver
uses the same CRC polynomial to compute the CRC
checksum, and compares the computed value with the
received value.
Timing
The PIC MCUs and dsPIC DSCs have several
dedicated communication interfaces, such as UART,
I
2
C™ and SPI modules. The IEC 60730 Class B
specifications suggest that these modules should use
time slot monitoring to ensure that the communication
occurs at the correct point in time.
Plausibility Check
The plausibility checks on the I/O periphery, analog
multiplexer and A/D convertor can be performed as
follows:
I/O PERIPHERY
The plausibility check on an I/O pin can be performed
by toggling the I/O and checking the state of the pin.
ANALOG MULTIPLEXER
To verify the operation of the analog multiplexer, known
voltage values are applied to all channels. These
values are read and compared with the applied voltage
for verification.
A/D CONVERTER
To test the analog functions of the A/D converter, a
known external voltage is applied to the analog inputs.
The conversion results are then compared with the
applied voltage.
API FUNCTIONS FOR 8-BIT PIC MCUs
(PIC10/12/16)
This section lists and describes the API functions that
are available in the Class B Safety Software Library for
8-bit architecture (PIC10/12/16). The API functions are
listed below followed by their individual detailed
descriptions:
• SSL_8bit_CPU_RegisterTest
• SSL_8bit_PCtest
• SSL_8bit_EEPROMtest_CRC16
• SSL_8bit_RAMtest_MarchC
• SSL_8bit_RAMtest_MarchC_Minus
• SSL_8bit_RAMtest_MarchB