• The MCxxxx family of microcontrollers employs a common programming system to simplify system design and
  reduce new product development time. A program written for one member of the MCxxxx family can be re-used in any
  other MCxxxx microcontroller with few or no changes (see note [1]).

• Programs for the MCxxxx are assembled from a small but versatile set of operations. Each line of an MCxxxx program can contain an instruction, which consists of the instruction’s name followed by zero or more instruction operands. Detailed descriptions of the available instructions and their usage are provided below.

• MCxxxx microcontrollers are designed to be used in power-constrained environments and applications, and the
  MCxxxx programming system has been designed accordingly. While a MCxxxx microcontroller is in a sleep state, it
  consumes no power. Otherwise, power consumption is proportional to the number of instructions executed.

• [1] MCxxxx microcontrollers have varying features, pinouts, and program space limitations, described in the modelspecific datasheets. Some adaptation may be required to account for these model-specific differences.

Each line of an MCxxxx program must have the following structure:
LABEL CONDITION INSTRUCTION COMMENT

All components are optional, but must appear in the specified order if present. Examples of syntactically valid lines:

# This line is a comment.
loop: # until ACC is ten
teq acc 10
+ jmp end
mov 50 x2
add 1
jmp loop
end:
mov 0 acc # reset counter

Any text following a “#” symbol is ignored until the end of the line. Comments improve developer productivity by
allowing the behavior of code to be described in-line with the program itself.

Labels must appear first on a line, and are followed by a colon (“:”). Labels are used as jump targets by the jmp
instruction. Labels must begin with a letter and may contain alphabetic, numeric, and underscore characters.

All instructions in the MCxxxx programming language are capable of conditional execution. Prefixing an instruction with a “+” or “-” symbol will cause that instruction to be enabled or disabled by test instructions. When an
instruction is disabled by a test instruction, it will be skipped and will not consume power. Instructions with no prefix
are never disabled and always execute normally. All conditional instructions start in a disabled state. A test instruction
must be executed to enable conditional instructions.

Registers are used as sources and destinations for data manipulated by MCxxxx instructions. The set of registers
varies between MCxxxx models. It is an error to use a register in a microcontroller program if that register is not present on that microcontroller.

acc is the primary general-purpose register used for internal computation on MCxxxx family microcontrollers. All
arithmetic operations implicitly use and modify the value of acc.

dat is a second register available on some MCxxxx family members. It can be used in most contexts where acc
is permitted.

The internal registers of MCxxxx microprocessors (acc and dat, if available) are initialized to the value 0.

The pin registers (p0, p1, x0, x1, x2, x3) are used when reading from or writing to the pins of MCxxxx microcontrollers. Reading and writing through the pins allows a single MCxxxx microcontroller to communicate and coordinate
with other connected, compatible devices. Each pin on an MCxxxx family microcontroller functions as either a simple
I/O or XBus interface. Refer to the appropriate datasheet for details on pin functionality.

null is a pseudo-register. Reading from the null register produces the value 0. Writing to the null register has
no effect.

Each type of instruction requires a fixed number of operands. If an instruction has any associated operands, they
must appear following the instruction name, separated by spaces. For the benefit of development productivity, the
MCxxxx programming system does not require the use of redundant punctuation to separate instruction operands.


Instruction operands are described with the following notation:

nop
This instruction has no effect.

mov R/I R
Copy the value of the first operand into the second operand.

jmp L
Jump to the instruction following the specified label.

slp R/I
Sleep for the number of time units specified by the operand.

slx P
Sleep until data is available to be read on the XBus pin specified by the operand.

Registers can store integer values between -999 and 999, inclusive. If an arithmetic operation would produce a
result outside this range, the closest allowed value is stored instead. For example, if acc contains the value 800 and
the instruction add 400 is executed, then the value 999 will be stored in acc.

add R/I
Add the value of the first operand to the value of the acc register and store the result in the acc register.

sub R/I
Subtract the value of the first operand from the value of the acc register and store the result in the
acc register.

mul R/I
Multiply the value of the first operand by the value of the acc register and store the result in the acc
register.

not
If the value in acc is 0, store a value of 100 in acc. Otherwise, store a value of 0 in acc.

dgt R/I
Isolate the specified digit of the value in the acc register and store the result in the acc register.

dst R/I R/I
Set the digit of acc specified by the first operand to the value of the second operand.

Examples of the dgt and dst instructions: