LCALL

LCALL, short for Long Call, is an instruction in the 8051 family of microcontrollers used to call a subroutine located at a 16-bit address in code memory. It is a three-byte instruction consisting of the opcode and two address bytes. When executed, LCALL pushes the address of the next instruction onto the hardware stack and then transfers control to the specified 16-bit address.

This capability allows subroutine calls to locations anywhere within the program memory, including addresses outside the current 2K code page. LCALL is typically used for modular programs where subroutines may reside in different memory regions or when code is organized across pages. After the subroutine completes, a RET instruction returns control to the instruction following the original LCALL.

In relation to other 8051 control instructions, LCALL is contrasted with ACALL (Absolute Call), which also pushes the return address but can only call within the current 2K code page using an 11-bit address. LJMP (Long Jump) transfers control to a 16-bit address without pushing a return address, so it cannot be used to return to the caller. AJMP (Absolute Jump) uses an 11-bit address within the current 2K page and does not stack the return address.

Example: LCALL 0x1234 would call the subroutine located at code address 1234h, with execution resuming at RET in the subroutine after it completes.

See also: 8051 instruction set, ACALL, AJMP, LJMP, RET.