Originally introduced in the mids, the architecture is an enhancement of the Freescale 68HC Programs written for the HC11 are usually compatible with the HC12, which has a few extra instructions. Unlike the 68HC11 the processor has 16bit internal data paths. The 68HC12 adds to and replaces a small number of 68HC11 instructions with new forms that are closer to the processor. More significantly it changes the instruction encodings to be far more dense and adds many like indexing features, some with even more flexibility.
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Hardware Reference. In-Depth Information. Instruction dbnz 0x21,loop machine code 5 D5 21 0A. Step 1. The value in the PC 0x is placed on the program memory address bus with a request. Step 2. The 8-bit value at the location 0x is the instruction opcode 0xD5. At the end of this. The program memory returns the opcode.
Step 3. The CPU recognizes that it needs to read a data memory address and a branch offset from. Step 4. Processor X performs two more read operations to the program memory. The program. At the end of these two read cycles,. Step 5. Processor X places 0x21 on the data memory address bus with a read request.
At the end. Step 6. Processor X decrements the contents of the MDR. The contents of the MDR are then placed. Processor X also places the address 0x21 on the data memory. Step 7. Otherwise, the PC is not changed.
This section demonstrates the activities that may occur during the execution of a program. Overall, the operations performed by the processor are dictated by the opcode. Freescale designed the 68HC12 as an upgrade to the 8-bit 68HC11 microcontroller. Motorola discovered that the performance of the 68HC12 microcontroller was not satisfactory. The 68HC12 has the highest bus clock speed of 8 MHz. The revised 68HC12 was referred to as the Star12 family.
It was. However, many of the internal designs have been changed. Automotive and process control applications are the two major target markets of the. This is evidenced by the inclusion of such peripheral functions as input capture IC ,. Other peripheral functions such as serial peripheral interface. Using flash memory to hold application programs has become the trend of microcontroller. All HCS12 members incorporate on-chip flash memory to hold programs.
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