Echelon Neuron - Manual (Page 61)

also supports a string format, but does not automatically include the
terminating zero-byte. An alternative declaration would have been
_%MYDEVICE%STR1 DATA.B “ABCDEFGH”, 0.
3. In the second code segment (SEG CODE), the Testcall() function
(%Testcall APEXP), uses the ALLOC #1 instruction to allocate one
local variable on the data stack (for the unsigned cs local variable). It
then pushes the address of the string onto the stack using the immediate
push-double instruction PUSHD #_%MYDEVICE%STR1, followed by a
PUSH #8 instruction for the size parameter. Note that the value 8 is out
of range for the shorter PUSHS instruction (which has a 1-byte opcode),
so the PUSH instruction must be used instead (which has a 2-byte
opcode).
4. Then, the Checksum function is called with the CALLF instruction, a far
call that can target any location in the 64 KB address space.
5. Finally, the compiler assigns the function result (in TOS) to the local
variable (in NEXT) with a simple DROP NEXT instruction. The cs local
variable is now in TOS. With the end of the block (indicated by the
closing curly brace), the compiler-generated code frees the allocated stack
space with the DEALLOC #1 instruction. The DEALLOC instruction
also performs a return-from-call operation (equivalent to RET).
Data Representation
The following sections describe how various types of data are represented in the
Neuron assembly language. The data types described include integers,
characters, strings, multi-byte objects, arrays, structures, unions, and bitfields.
Integers, Characters, and Strings
Short integers and characters are stored as a single byte. The Neuron assembly
representation of a signed integer is in two's-complement form; thus, the same
instructions can be used for both signed and unsigned arithmetic. A variety of
firmware functions are used for other arithmetic operations, as described in
Chapter 8, System-Provided Functions.
A character string is an array of characters (thus, an array of bytes). Strings
that interface with Neuron C are expected to include a terminator byte of zero.
Each Neuron C global or static variable is defined as its own relocatable segment
within the appropriate segment type.
Multi-Byte Values
Multi-byte scalar objects (such as signed and unsigned long integers) are stored
as two consecutive bytes in big endian orientation: the most significant byte is
stored at the lower address. Whenever a long integer is pushed onto the data
stack, the most significant byte is pushed first (or popped last).
Neuron Assembly Language Reference 51