Turbo51 Memory Organization

Pascal Compiler for 8051 microcontrollers

CODE memory

By default the maximum code size is $10000 bytes (64 KB). This can be changed in the main program with the $M directive.

IDATA memory

By default there is no IDATA memory. This can be changed either in the main program or in one of the directly or indirectly used units with the $IDATA directive. Usualy the main program uses a unit which declares features of the microcontroller including the IDATA memory with the $IDATA directive.

XDATA memory

By default there is no XDATA memory. This can be changed either in the main program with the $M directive or in one of the used units with the $XDATA directive.

DATA / IDATA Memory organization

If compiler switch $I is set then IDATA variables immediately follow DATA varables. If there is no IDATA memory or IDATA variables then stack immediately follows DATA variables. IDATA variables can start below $80 if there is free DATA memory and the $I directive is on.

Register bank 0	$00..$07
Register bank 1	$08..$0F
Register bank 2	$10..$17
Register bank 3	$18..$1F
Boolean variables	$20
Bit-addressable DATA variables
DATA variables
Free DATA memory
	$80 - First IDATA address
IDATA variables
StackStart	Last variable (dummy)
Stack
	End of DATA / IDATA memory

XDATA Memory organization

Start address and size of XDATA memory and heap size can be set with compiler directive M ($M<CODE Start>, <CODE Size>, <XDATA Start>, <XDATA Size>, <Heap Size>).

	XDATA memory start (first byte)
XDATA Variables
XDATA_StackStart	Last XDATA variable (dummy)
XDATA Stack
Free XDATA Stack (first byte)	XSP
Free XDATA Stack
	HeapOrg - first byte of heap
HEAP
Free HEAP (first byte)	HeapPtr points to the address of unused heap block
Free HEAP
	HeapEnd - XDATA memory end (last byte)