UPSD3212A(2009) 데이터 시트보기 (PDF) - STMicroelectronics

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UPSD3212A
(Rev.:2009)

Flash programmable system devices with 8032 MCU and USB and programmable logic

STMicroelectronics 

UPSD3212A, UPSD3212C, UPSD3212CV

Architecture overview

The LJMP instruction encodes the destination address as a 16-bit constant. The instruction

is 3 bytes long, consisting of the opcode and two address bytes. The destination address

can be anywhere in the 64K Program Memory space.

The AJMP instruction encodes the destination address as an 11-bit constant. The

instruction is 2 bytes long, consisting of the opcode, which itself contains 3 of the 11 address

bits, followed by another byte containing the low 8 bits of the destination address. When the

instruction is executed, these 11 bits are simply substituted for the low 11 bits in the PC. The

high 5 bits stay the same. Hence the destination has to be within the same 2K block as the

instruction following the AJMP.

In all cases the programmer specifies the destination address to the assembler in the same

way: as a label or as a 16-bit constant. The assembler will put the destination address into

the correct format for the given instruction. If the format required by the instruction will not

support the distance to the specified destination address, a “Destination out of range”

message is written into the List file.

The JMP @A+DPTR instruction supports case jumps. The destination address is computed

at execution time as the sum of the 16-bit DPTR register and the Accumulator. Typically.

DPTR is set up with the address of a jump table. In a 5-way branch, for ex-ample, an integer

0 through 4 is loaded into the Accumulator. The code to be executed might be as follows:

MOV DPTR,#JUMP TABLE

MOV A,INDEX_NUMBER

RL A

JMP @A+DPTR

The RL A instruction converts the index number (0 through 4) to an even number on the

range 0 through 8, because each entry in the jump table is 2 bytes long:

JUMP TABLE:

AJMP CASE 0

AJMP CASE 1

AJMP CASE 2

AJMP CASE 3

AJMP CASE 4

Table 13 shows a single “CALL addr” instruction, but there are two of them, LCALL and

ACALL, which differ in the format in which the subroutine address is given to the CPU. CALL

is a generic mnemonic which can be used if the programmer does not care which way the

address is encoded.

The LCALL instruction uses the 16-bit address format, and the subroutine can be anywhere

in the 64K Program Memory space. The ACALL instruction uses the 11-bit format, and the

subroutine must be in the same 2K block as the instruction following the ACALL.

In any case, the programmer specifies the subroutine address to the assembler in the same

way: as a label or as a 16-bit constant. The assembler will put the address into the correct

format for the given instructions.

Subroutines should end with a RET instruction, which returns execution to the instruction

following the CALL.

RETI is used to return from an interrupt service routine. The only difference between RET

and RETI is that RETI tells the interrupt control system that the interrupt in progress is done.

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