[机械模具数控自动化专业毕业设计外文文献及翻译]【期刊】基于MCS-51单片机结构中16MB寻址空间的设计-外文文献

Design of 16MB Addressing Spaces in an MCU Based on the MCS-51 Structure JING Wei-liang, HU Yue-li, CAO Jia-linMicroelectronic Research and Development Center, Shanghai University NO.149, Yanchang Road, Shanghai 200072, China Email:, Phone:086Abstract: This paper presents the design of 16M-byte addressing spaces in an MCU (Micro-control Unit) based on the structure of MCS-51. Both external data and program storage capacities are enlarged from 64K to 16M bytes without the increment of time-multiplexed address buses and the change of the whole instruction set. Thereby, a large number of data and programs with complex algorithms can be processed and run on this MCU. After the successful simulation at the front end, practical experiments made on a Nios development board verify that the design is correct. Furthermore, the design gains good effects in practical applications and enables the MCU to control an image processing system with much more than 64KB programs and tremendous data. Index terms: MCS-51, MCU, Program Counter, Program Address, Addressing space. 1. Introduction A SCMP (Single-Chip MultiProcessor) structure is employed in our “Skin Diagnoses” machine vision chip. Each slave processor has its own responsibility, including common algorithms of machine vision, database and knowledge-base management and etc, without users participating in, while a master processor faces users directly. The instruction set is completely compatible with that of MCS-51 so that it is the same as executing MCS-51 instructions for users to process certain image processing algorithms. System application engineers neednt to learn professional knowledges of image processing, machine vision training and programming to achieve some functions concerned, so it is very easy to use machine vision technologies in all kinds of MCU fields.To achieve the objective described above, an MCU, able to control and handle intricate computations, is required. And it is the core and basic part of the machine vision chip. As is known to all, MCS-51 has a long history of usage, a variety of application fields and plentiful supplies of third-party software and simulation tools. Therefore, an MCU with the structure of MCS-51 is designed. But the data space and the program capacity of MCS-51 are only 64KB respectively1. Such sizes cannot meet the requirements of tremendous data and complex Foundation item: Project supported by the Science Foundation of Shanghai Municipal Commission of Education (Grant No.03AK16); Key Technology Foundation of Shanghai Municipal Commission of Science and Technology (Grant No.025911323 ). Communication author: HU Yue-li. algorithms of image processing. If the addressing spaces of 51MCU can be enlarged without changing the instruction set and the definitions of ports or pins, the performance of MCUs with the MCS-51 structure will be largely improved and enhanced. The paper puts forward a time-multiplexed method and implements the design of both 16MB data and 16MB program addressing spaces. 2. Design of 16MB addressing spaces 2.1Ideas 2.1.1 Data Memory A 8-bit SFR (Special Function Register) DPTR_PAGE is added as the page address of an external 16MB data memory in order to enable the MCU to access this 16MB space. Each page size is 64KB and the 16MB data memory is divided into 256(28) pages. The addressing method in every page is the same as that of a standard MCS-51. The page address is sent out by PORT2 as the highest 8 bits. The middle 8-bit address and the low 8-bit address are sent out by PORT2 and PORT0 just as a standard 8051 transmits its 16-bit address. Fig.1 External Data Memory connected to an MCU The connecting method of the MCU and its external data memory is shown in Fig.1. Address Latch 1 latches the low 8-bit address and Address Latch 2 latches the high 8-bit address. The middle 8-bit address is sent out after the high 8 bits are latched. 2.1.2 Program Memory To enable an MCU to access a 16MB program memory, two design ideas are conceived of at the very beginning: One is to change the instruction set. For example, original LCALL/LJMP addr16 instructions have 16-bit operands. We can change them to LCALL/LJMP addr24 instructions with 24-bit operands and enable a PA(Program Address) to jump to another program module or to call another sub-module freely in 16MB addressing spaces. This modification is relatively easy with regard to design issues, but standard MCS-51 compilers must be modified or even redesigned. Authorized licensed use limited to: Guangdong Univ of Tech. Downloaded on May 22,2010 at 11:44:47 UTC from IEEE Xplore. Restrictions apply. Otherwise, the original instruction set in standard compilers cannot be decoded correctly. Thus, MCUs with such a modified instruction set are lack of compatibility for usage and not beneficial to their spread and application. The other one is to divide a program memory logically without changing any MCS-51 instruction. The space of an addressable 16MB program storage comprises 256 blocks and each block address determines the highest 8 bits of a 24-bit address. Any particular address in each 64KB block consists of the middle 8 bits and the low 8 bits of a 24-bit PA. A PC (Program Counter) keeps the low 16 bits of a PA. Fig.2 Structure of Program Memory Spaces To make the MCU to be designed have better compatibility, we adopt the second means by which the standard MCS-51 instruction set is not changed and additional 8-bit address lines are not added. Fig.2 shows the structure of extended program memory addressing spaces.2.2 16MB addressing spaces of a Data Memory 2.2.1 Data Pointer Register (DPTR) A data pointer is composed of three 8-bit registers, namely DPTR_PAGE, DPTR_LOW and DPTR_HIGH. The address of DPTR_PAGE is 95H and this register can be customized by users. It stores the high 8 bits of a 24-bit PA. The addresses of DPTR_LOW/DPTR_HIGH are 82H and 83H. And both of these two registers can also be customized by users. They keep the low 8 bits and the middle 8 bits of a 24-bit PA. 2.2.2 Automatic Detecting Logic This work proposes a cross-page approach implemented with an automatic detecting logic. A DEC DPTR instruction, whose address is A5H, is added to the MCU. When the MCU accesses an external data memory, INC DPTR/DEC DPTR instructions may cause the value of the low 16 bits of DPTR to be changed from FFFFH to 0000H or from 0000H to FFFFH and a cross-page situation may take place. An automatic detecting logic will increase or decrease the content of DPTR_PAGE by one under such situations and thus the data can be correctly written into or read out of a previous or next page of a 16MB data memory. Some parts of the codes implementing the cross-page function are shown in Fig.3. PC_CON0 is a decoding signal of the INC_DPTR instruction and PC_CON1 is a decoding signal of the DEC_DPTR instruction. CCLK signal is a working clock of the MCU. Fig.3 Partial codes of an Automatic Detecting Logic 2.3 16MB addressing spaces of a Program Memory In the MCU, PC/PA/PRO_BLOCK/DPTR control modules are designed to compute and store the address of the next instruction storage unit. The generation of a 8-bit block address, the formation of a 24-bit PA and the operation of a 16-bit PC and DPTR are controlled and managed by these four parts. 2.3.1 PA (Program Address) & PC (Program Counter)To accelerate the processing rate of the MCU, a Prefetching Technique is employed. The 24-bit address of the next instruction is read out at the third phase during the last machine cycle of a current instruction. Each internal unit address of a program memory comes from a PA according to which all addresses of both instruction operation codes and operands are transmitted and stored. When the MCU is reset or supplied with power, the initial value of a 24-bit PA is 000000H. A program counter (PC) is a 16-bit special register and can enable the MCU to address a 64KB space. When the MCU is reset or supplied with power, the initial value of a 16-bit PC is 0000H. The PC register is independent and cannot be accessible to users2.The low 16 bits of a PA are the same as the whole 16 bits of a PC except when MOVCS instructions are processed. For example, as the MOVC A, A+PC or MOVC A, A+DPTR instruction is being run, the PC doesnt change, while the content of the PA must be changed to the value of (A+PC) or (A+DPTR) so that the MCU can read data at the updated address and assign them to the Accumulator. So the control logic circuit of a PC differs a little from that of a PA.2.3.2 Block Address Generator The block address generator is responsible for generating the high 8 bits of a PA, so whether the sequential design of block address sources is correct or not directly determines whether programs can be run correctly or not. The address of blocks has three sources Authorized licensed use limited to: Guangdong Univ of Tech. Downloaded on May 22,2010 at 11:44:47 UTC from IEEE Xplore. Restrictions apply. except the default value 00H: the content users can customize; the data from an external or internal PA stack after RET/RETI instructions are processed; the updated block address after programs jump relatively across adjacent blocks. See Fig.4: Structure of a Block Address Generator. Fig.4 Structure of a Block Address Generator PRO_BLOCK SFR Users should define the address of certain block before the LJMP/LCALL instructions are processed in order to jump across blocks or to call sub-modules located in other blocks. The detailed method of achieving this target is to add a new SFR called PRO_BLOCK in the MCU. Its address is FFH. And its value will be set to 00H after the system is reset. Users can write a 8-bit block address into this SFR before running LJMP/LCALL instructions. In Fig.4, PRO_BLOCK_W is a write-enable signal and REG_RESULT stores the block address customized by users. Block address after Interrupt/CallingAs is shown in Fig.4, XRAMDI stores the value of a block address to be popped out from the stack of an external data memory while SOURCE_DI stores the value of a block address to be popped out from the stack of an internal data memory. At the end of RET/RETI instructions, block addresses originally stored in an external or internal memory are popped out from either stack and transmitted to the PRO_BLOCK SFR. Automatic Increment of a Block address In Fig.4, the next block address value (PRO_BLOCK + 1) is stored in ROM_0. When programs run orderly through two adjacent blocks, the value of the PRO_BLOCK SFR is automatically updated to that of ROM_0 and the MCU can correctly fetch the next operation code or operand at the beginning of the next block. Block address after Relative JumpingThe previous block address value (PRO_BLOCK - 1) is stored in ROM_1 shown in Fig.4. When programs jump relatively to a previous block, the value of the PRO_BLOCK SFR is automatically updated to that of ROM_1. And when programs jump relatively to the next block, the value of PRO_BLOCK is changed to ROM_0. 3. Simulation & Verification 3.1 Simulation on a workstationThe soft core is simulated relatively thoroughly on a workstation (SUNW, Ultra-60; sparc; sun4u). The simulation tool is Verilog-XL (Cadence). A part of assembly language codes testing CJNE instructions is described in Fig.5. The objective of this test_bench is to verify that the design of 16MB program addressing spaces is correct. When certain program runs orderly through two adjacent blocks, the value of PRO_BLOCK can increase by one automatically. And any program can jump relatively in every block or across blocks not only freely but also correctly. Fig.5 Testing codes of CJNE instructions The waveforms of testing results are shown below. STATE is a signal of the MCU state machine and PROGA is the same as a 24-bit PA. Fig.6 CPL 0D3H Fig.6 is the beginning waveform of the testing codes. PORT0 transmits data and the low 8 bits of a PA every other phase. B2 D3 is the machine code of CPL 0D3H. Authorized licensed use limited to: Guangdong Univ of Tech. Downloaded on May 22,2010 at 11:44:47 UTC from IEEE Xplore. Restrictions apply. Fig.7 CJNE R0, #01H, ADD0 In Fig.7, B6 01 66 is the machine code of CJNE R0, #01H, ADD0. At the end of this instruction, PROGA shows the address of ADD0 1900C4H and MOV P1, 0D0H will be processed. Fig.8 MOV P1, 11H In Fig.8, B5 11 90 is the machine code of MOV P1, 11H. As instructions such as those jumping or calling ones are not processed, PROGA increases by one automatically from BLOCK_19 to BLOCK_1A. Fig.9 CJNE R1, #0E7H, ADD4 In Fig.9, B7 E7 F2 is the machine code of CJNE R1, #0E7H, ADD4. At the end of this instruction, PRO_BLOCK decreases by one automatically from BLOCK_1A to BLOCK_19. Jumping relatively across adjacent blocks is achieved. 3.2 FPGA VerificationThe soft core is also verified on an Altera Nios FPGA development board. One certain testing environment is described as below: External interrupt source zero (IT0) is set to have priority over external interrupt source one (IT1). The valid signal of IT1 appears before that of IT0 while the main program is running. And as the IT1 sub-module is being processed, the valid signal of IT0 takes place. IT1 has a lower priority, so its interrupt sub-module will be suspended and the interrupt sub-module of IT0 will be executed. When the sub-module of IT0 is finished, the PA will be changed to where the IT1 sub-module has been stopped and the module will continue to be processed until the end of this sub-module. By that time, the main program will have been activated again. IT0 & IT1 is supplied by two ping-pang keys on the Nios board. The function of the IT1 sub-module is to make LED show number 1 orderly M times while the IT0 sub-module lets LED show number 0 orderly N times (MN). The function of the main program is to activate a buzzer on the board. The addresses of interrupt entrances are both located at block_0 and these three modules are put in different blocks. After the design passes the compiling and simulation on QUARTUS (Altera), the RTL(Register Transfer Level) codes of the MCU are programmed into FPGA and the testing machine codes are put into a FLASH memory on the board. The objective of this experiment is to verify that the program pointer can return to BLOCK_0 and the 24-bit PA can be correctly pushed into or popped out of a stack. The results of the experiment are the same as what we have expected and the design achieving this function is proved to be correct. 4. Conclusions An MCU with both 16MB data and 16MB program addressing spaces is designed based on the MCS-51 structure. The instruction set is totally compatible with that of standard 8051, so those tools and thirty-party software that support the 51 series can all be used. The design is verified to be correct after the simulation on a workstation and the verification through FPGA. As an IP (Intellectual Property) core, the MCU has been embedded into an image processing system chip with the structure of SCMP (Single-Chip Multiprocessor). The advanta