| The Development of 8-bit MCUs from Cygnal C8051F
Author: He Limin, Beijing University of Aeronautics and Astronautics
Abstract: 80C51 is a unique 8-bit MCU series. From Intel's early MCS-51 to the 80C51 series MCUs developed by PHILIPS, ATMEL and other companies, and then to the latest C8051F launched by Cygnal, it shows the typical development process of MCUs. Cygnal's C8051 has SoC characteristics and integrates many advanced technologies of embedded systems. These advanced technologies will promote the development of 8-bit MCUs.
Keywords: C8051F CIP-51 Cross switch JTAG interface SoC
In the field of low-end MCUs in embedded systems, it has been nearly 30 years since the birth of 8-bit MCUs. In the flourishing MCU family, the 80C51 series has always played a unique role. Cygnal's launch of C8051F has attracted the attention of industry insiders. Looking back at history, soon after Intel launched MCS-51, it implemented the most thorough technology opening policy; with the active participation of many electrical and semiconductor manufacturers, MCS-51 was developed into the 80C51 MCU family with many models and series. The classic architecture, excellent compatibility and open policy of MCS-51 not only attracted many manufacturers to participate in the development, but also induced semiconductor manufacturers to carry out any transformation of MCS-51. Due to the best compatibility provided by MCS-51, MCS-51 can maintain the life of 8051 core with unchanged instruction system and compatibility of basic units after being "dismembered" and will play the important role of 8-bit CPU core in the future SoC development. Looking back at the process of 80C51 series from MCS-51, 80C51 to C8051F, we can deeply understand some regularities in the development of single-chip microcomputers.
1. The 8-bit machine phenomenon in embedded applications
Compared with general-purpose computers that have rapidly transitioned from 8-bit machines to 16-bit, 32-bit, and 64-bit machines, 8-bit single-chip microcomputers have been the main model for low-end embedded applications since their birth in the early 1970s, although they have undergone changes from single-chip microcomputers to microcontrollers, MCUs, and SoCs, and they will continue to maintain this momentum for a long time in the future. This is because embedded systems and general-purpose computer systems have completely different application characteristics, thus heading towards completely different technical development paths.
Embedded systems are embedded in object systems and run in object environments. The operations related to the object field are mainly to collect and process external physical parameters, control external objects, and interact with operators. However, the response speed required for the collection and processing of physical parameters in the object field, the control of external objects, and human-computer interaction is limited and will not change over time. After the 8-bit single-chip microcomputer can basically meet its response speed requirements, the data width will not become the main contradiction in technological development. Therefore, the 8-bit single-chip microcomputer will stabilize, and its technical development direction will turn to maximize the satisfaction of object collection, control, reliability, low power consumption and other quality requirements.
With the development of modern communication technology, the growth of intelligent system's demand for DSP requires the microcontroller to improve its operation speed accordingly. At present, there is still potential for improving the operation speed of 8-bit microcontrollers without expanding the data bus. For example, the RISC structure is used to realize parallel pipeline operation, and the C8051F with CISC structure adopts the CIP-8051 structure, which increases the single-cycle instruction speed to 12 times that of the original 8051.
In view of the limited response requirements of low-end embedded application objects, the huge market for low-end applications of embedded systems, and the speed potential of 8-bit machines, it can be expected that 8-bit machines will remain the mainstream model in embedded applications for a long time in the future.
With the development of semiconductor technology, 8-bit microcontrollers will develop rapidly in CPU structure, CPU peripherals, functional peripherals, peripheral interfaces and integrated development environments; therefore, it can be said that although 8-bit microcontrollers are "old", they will be a very active and emerging embedded field. The development process of the 80C51 series from Intel's MCS-51 to Cygnel's C8051F fully illustrates this point.
2. The 80C51 phenomenon in 8-bit microcontrollers
Among 8-bit microcontrollers, the 80C51 series has formed a unique landscape. With the longest history, it has been prosperous for a long time, and has been constantly updated, forming a microcontroller series that is both classic and full of vitality. At present, the C8051F launched by Cygnal has pushed the 8051 compatible microcontroller to the forefront of 8-bit machines. Summarizing the development history of the 80C51 series, we can see that there have been three technological leaps in microcontrollers.
2.1 The first leap from MCS-51 to MCU
The MCS-51 launched by Intel in 1980 laid the foundation for the classic architecture of single-chip microcomputers for embedded applications, but soon abandoned further development plans and implemented a technical opening policy for 8051. Whether from subjective or objective factors, it is a wise move. Because after creating a complete embedded computer architecture, it is faced with various control functions that continuously meet the requirements of embedded objects. After the 8051 was opened, PHILIPS, as a world-renowned electrical appliance manufacturer, focused on developing the control functions and peripheral units of 80C51 with its advantages in electronic application systems. The single-chip microcomputer of MCS-51 was quickly promoted to the MCU era of 80C51, forming a series of single-chip microcomputer products that can meet a large number of embedded applications.
2.2 The second leap leading the Flash ROM trend
At present, embedded systems generally use Flash ROM technology. The use of Flash ROM has accelerated the development of single-chip microcomputer technology. The ISP/IAP technology based on Flash ROM has greatly changed the structural mode and development and operation conditions of single-chip microcomputer application systems; and the first to implement Flash ROM technology in single-chip microcomputers was the AT89Cxx series of ATMEL. 2.3 The third leap of core SoC
The typical architecture and excellent compatibility of MCS-51 have formed a good structural mode of embedded processor core for the continuously expanding periphery of MCU. At present, embedded system applications have entered the SoC mode, and have entered the SoC from various angles and in different ways, forming a boom in embedded system applications. In this technological trend, 8051 plays an important role as the core of embedded systems. In the process of digital and analog hybrid integration from MCU to SoC, ADI launched the ADμC8xx series, while Cygnal realized the transition to SoC's C8051F; in the process of PLD's development to SoC, Triscend used 8052 as the processor core in the E5 series of configurable system-on-chip CSoC.
3. Cygnal C8051F's technological breakthrough over 80C51
We are accustomed to calling the various single-chip microcomputer series compatible with 51 produced by various manufacturers the 80C51 series. They all use CMOS technology and are compatible with MCS-51.
Compared with MCS-51, 80C51 has made great progress. However, the C8051F series currently developed by Cygnal has exceeded the current 8-bit single-chip microcomputer level in many aspects, and there are many new technical concepts that need to be learned and updated.
3.1 Using CIP-51 core to greatly improve the speed of CISC structure.
So far, MCS-51 has become the slowest series of 8-bit machines. In order to improve the speed, DALLAS and PHILIPS adopted the traditional method of changing the bus speed, shortening the machine cycle from 12 to 4 and 6, but the speed improvement was limited.
Cygnal has taken a new approach to improve the speed of 8051, that is, to try to implement pipeline operation for instruction operation while keeping the CISC structure and instruction system unchanged, and launched the CIP-51 CPU mode. In this mode, the concept of machine cycle is abolished, and instructions are run in clock cycles. On average, one single-cycle instruction can be executed per clock, which greatly improves the instruction running speed. That is, compared with 8051, the single-cycle instruction running speed is 12 times that of the original under the same clock; the average running speed of the entire instruction set is 9.5 times that of the original 8051, making the 8051 compatible machine series enter the ranks of 8-bit high-speed microcontrollers.
3.2 I/O from fixed mode to cross switch configuration
So far, most I/O ports are fixed as input/output ports of a special function, which can be single-function or multi-function. I/O ports can be programmably selected as unidirectional/bidirectional, pull-up, open-drain, etc. Fixed I/O ports occupy many pins and are not flexible in configuration. To this end, Scenix Company adopted the virtual peripheral method to transform the fixed mode of I/O into software setting mode in the 8-bit SX microcontroller series it launched. In Cygnal's C8051F, a switch network is used to implement flexible configuration of I/O ports in hardware, as shown in Figure 1. In this I/O port system configured by a cross switch, the outside of the microcontroller is a general I/O port, such as P0, P1 and P2. The circuit units with input/output are configured to the selected port through the cross switch controlled by the corresponding configuration register.
Figure 1
3.3 From system clock to clock system
Early microcontrollers used one clock to control all timings in the chip. After entering the CMOS era, due to the requirements of low-power design, the CPU running speed under one master clock can be selected to operate at different clock frequencies; or set to high and low master clocks, select the appropriate clock speed according to the system operation requirements, or turn off the clock. Cygnal's C8051F provides a complete and advanced clock system, as shown in Figure 2. In this system, a programmable clock oscillator is set on the chip (no external device is required), which can provide programming settings of 2, 4, 8 and 16 MHz clocks. There are 4 ways to select the external oscillator. When the program is running, the internal and external clocks can be dynamically switched. In addition to being used on the chip, the programmed clock output CYSCLK can also be output from any selected I/O port.
Figure 2
3.4 From traditional simulation debugging to in-system debugging based on the JTAG interface
C8051F is the first 8-bit microcontroller to be equipped with a standard JTAG interface (IEEE1149.1). The introduction of the JTAG interface will bring about a complete change in the traditional simulation debugging of 8-bit microcontrollers. With the support of the host computer software, the product system can be directly simulated and debugged through the serial JTAG interface. The JTAG interface of C8051F not only supports the read/write operation of Flash ROM and non-intrusive in-system debugging, but its JTAG logic also provides boundary scan function for in-system testing. Through the programming control of the boundary register, the weak pull-up function of all device pins, SFR bus and I/O port can be observed and controlled.
3.5 From pin reset to multi-source reset
In non-CMOS microcontrollers, usually only one method of pin reset is provided. So far, the 80C51 series microcontrollers still remain at this level. For the safety of the system and the power consumption management of CMOS microcontrollers, higher and higher requirements are put forward for the reset function of the system. Cygnal's C8051F develops the single external reset of 80C51 into a multi-source reset, as shown in Figure 3. The multiple reset sources of C8051 provide power-on reset, power-off reset, external pin reset, software reset, clock detection reset, comparator 0 reset, WDT reset and pin configuration reset. The numerous reset sources bring great benefits to the safety of the system, the flexibility of operation and the design of zero-power system.
Figure 3
3.6 The best support for the system with minimum power consumption
In the CMOS system, according to the characteristics of the CMOS circuit, the system power consumption WS is
WS = CV2f
where: C is the load capacitance, V is the power supply voltage, and f is the clock frequency.
C8051F is the first 8-bit microcontroller to get rid of 5 V power supply, and realizes 3 V power supply (voltage range 2.7~3.6 V) for on-chip analog and digital circuits, greatly reducing system power consumption; the perfect clock system can ensure that the system has the lowest average clock frequency while meeting the response speed requirements; numerous reset sources allow the system to wake up at will in power-down mode, so that zero-power system design can be flexibly implemented. Therefore, C8051F has an excellent minimum power consumption system design environment.
Although C8051F has gotten rid of 5 V power supply, it can still be easily connected to 5 V circuits. All I/O ports can receive 5 V logic level inputs, and can also drive 5 V logic devices after selecting open drain and adding pull-up resistors to 5 V.
4. 8051 core makes further contributions in SoC
SoC is the final form of embedded application system. In embedded system applications, in addition to the most basic and widely used microcontrollers, EDA models based on PLD and hardware description languages, and microelectronics ASIC models based on IP libraries have formed many SoC solutions. Whether it is microelectronic integration, programmable design of PLD, or analog hybrid integration of single-chip microcomputer, the goal is SoC, and the means will gradually form a mode based on processor core plus peripheral IP unit. As an 8-bit classic structure, 8051 has begun to be recognized by many manufacturers and is widely used in the processor core of SoC.
4.1 8051 core from single-chip
microcomputer to SoC The development of single-chip microcomputer from single-chip microcomputer to microcontroller (MCU) reflects the development direction of single-chip microcomputer to SoC, and continuously expands peripheral functions, peripheral interfaces and analog and digital hybrid integration required by the system according to system requirements. In the process of developing to SoC, many manufacturers introduced 8051 core to form SoC single-chip microcomputer. For example, after introducing 8051 core, ADI configured its own advantageous product-signal conditioning circuit to form SoC for data acquisition; Cygnal configured comprehensive system drive control and forward/backward channel interface for 8051, forming a more comprehensive general-purpose SoC.
4.2 SoC application of 80C51 core in PLD
Based on PLD, electronic system designed with hardware description language is a very popular method in recent years. When solving large-scale intelligent systems, a large number of programmable logic gates are required. This leads to a large design workload, it is difficult to fully utilize resources, and the probability of error is also high. With the development of IP cores and processor technology, companies engaged in programmable logic devices, when moving towards SoC, almost always integrate microprocessors, storage units, and general IP modules into PLDs to form configurable SoC chips (CSoC). When designers use such chips to develop products, since 80% of the components required for system design are already integrated on CSoC, designers can save a lot of energy. The E5 series SoC launched by Triscend is composed of an 8051 processor core, plus 40 KB RAM, WDT, DMA, and a 40,000-gate PLD with an SoC bus, forming a programmable semi-custom SoC device with 8051 as the core.
4.3 Application of 8051 core in programmable select SoC (PSOC) devices
The idea of constructing a product SoC based entirely on general IP modules and programmable selection was advocated and launched by Cypress. This programmable selection SoC is named PSoC, which consists of a basic CPU core and preset peripheral components. Cypress integrates a variety of digital and analog devices, microprocessors, processor peripheral units, and peripheral interface circuits into PSoC, and users only need to build their own product systems according to the functions of the product. Cypress chose 8051 when building the 8-bit processor in PSoC.
Conclusion
① In embedded applications, due to the characteristics of the application objects and environment, 8-bit machines have always occupied the mainstream position in low-end applications.
② In the family of single-chip microcomputers, MCS-51 is a unique series. Intel created the classic series structure of 8-bit machines and implemented a technology development policy, which made this series go through vicissitudes but not old.
③ PHILIPS and other famous large electrical appliance manufacturers, with their advantages in electronic application technology, complemented Intel's technology, developed MCS-51, and quickly brought single-chip microcomputers into the era of microcontrollers (MCU), created many excellent single-chip microcomputer products, and formed a unique 80C51 series that includes compatible products from many companies.
④ Cygnal launched the C8051F series, pushing the 80C51 series to a new height and bringing single-chip microcomputers from MCU to the SoC era. Some new technologies in C8051F will surely be further popularized and promoted in 8-bit machines.
⑤ MCS-51 has gone from single-chip microcomputers (SCMC) to microcontrollers (MCU) and then to system-on-chip (SoC) cores, showing the typical change process of embedded system hardware systems. In the final system of embedded system SoC, MCS-51 continues in the form of 8051 processor cores. For the vast number of people engaged in 80C51 teaching and scientific research at home and abroad, whether in the past, present or future, they can feel the benefits it brings.
＊This article is reprinted from the fifth issue of "Single-chip Microcomputer and Embedded System" magazine
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