CAN bus expanders MCP25050
Abstract: This paper describes MicroChip produced CAN bus I / O expansion device MCP25050 the main features, internal structure, pin definitions and working principle of the expansion with the MCP25050 CAN nodes typical application circuit diagram.
1 Overview
MicroChip company's CAN (Controller Area Net-work) bus I / O expansion device MCP25050, can be used to expand the CAN bus system CAN bus node, it can be independent without the need to form a CAN node plus microcontroller. The device a 14-pin small package and low power CMOS process technology, can be 2.7 ~ 5.5V voltage range of work. CAN2.0B it can support standard bit rates up to 1Mbit / s; NCP25050 shielding device includes a programmable , received two programmable filters, 4-way 10-bit A / D converter, PWM output Two, three automatic transmission data buffer, two receive data buffer and low-power work; its chip configuration information CAN bus line can be modified, and can work in 1-WireCAN bus mode; the same time, it also makes the system with remote input and output. Therefore, in the expansion of simple thin client CAN bus when the remote node, use it with to unexpected convenience.
CAN bus expanders MCP25050
2 MCP25050 internal structure
MCP25050 internal function diagram shown in Figure 1, pin diagram shown in Figure 2. Can be seen from the figure: the main user of the device storage area, clock generator, control logic, CAN protocol modules, A / D conversion and PWM module. The following were introduced:
Control logic to other parts of the main play the role of several parts joined together, while also sending and receiving control data and power on initialization of the internal registers of the control operation.
Part of the clock generator chip can be provided for the other clock pulse.
User store is a ROM area, mainly some control register, use it on the user storage area can first be programmed to enable the MCP25050 after power on reset the work in the pre-defined user mode. These registers can access the CAN bus.
A / D part is an analog input signal automatic A / D conversion.
CAN protocol modules mainly for CAN to send packets of data encapsulation, or the received CAN packets unpack. It has two independent of each other's receive buffer, and each has its own receive buffer receiver filter. Meanwhile, the fault management logic in this module. Thus, CAN protocol module is the core module MCP25050.
GPIO module using eight input and output pins can be managed, and can be made by setting the register to the work of each pin in a different way. MCP25050 shows the pin functions as listed in Table 1.
Table 1 MCP2505 pin Function
No. Pin Name pin multiplexing feature functions
GP0/AN0 1 bi-directional IO port analog input channel 0
GP1/AN1 2 bi-directional IO port analog input channel 1
GP2/AN2/PWM1 3 bi-directional IO port analog input channels 2/PWM output
GP3/AN3/PWM2 4 bi-directional IO port analog input channels 3/PWM output
GP4/VREF- 5 bi-directional IO reference power supply negative terminal
GP5/VREF 6 bi-directional IO port reference power supply positive terminal
No power supply ground VSS 7
OSC1/CLKIN 8 External crystal input the external clock signal input
OSC2 9 output without an external crystal
GP6/CLKOUT 10 bi-directional IO port clock signal output
GP7/RST/VPP 11 bi-directional IO port reset port
RXCAN 12 CAN data entry without
TXCAN / TXRXCAN 13 CAN 1-Wire data transmission sent under the receiver operating
No power supply VDD 14
3 Works
The MCP25050 power, the system will first enter the reset mode of operation, this time it will be closed to receive and send data at the same time, A / D converter and PWM are also prohibited; then MCP25050 for self-initialization, since the initialization mainly through the user data store read SRAM to achieve; when the self-initialization is completed, MCP25050 will enter normal operating mode, to prepare to receive or send data, then A / D converter and PWM can work; Next MCP25050 CAN bus made in a "line" signal to the network to notify existence of this site throughout the network.
MCP25050 devices through a universal screening, two receivers and two receive buffers the filter to determine whether the data received is accepted. MCP25050 There are three data types: information request data, output data and input data. In which the data refers to information requests MCP25050 received data, output data refers to the MCP25050 response to a request for information issued by the data, while the input data refers to the MCP25050 received data can be used to modify the register.
MCP25050 also has automatic transmission, it has three independent of each other to send data ID: TXID0, TXID1 and TXID2. Which TXID0 used to send "line" signals, TXID1 to send the "order confirmation" signal, the signal receiver and a buffer overflow error information, TXID2 is used to send A / D conversion results.
CAN bus expanders MCP25050
4 practical application
CAN bus system in the traditional, if need to add a node, the general practice is to use an MCU microcontroller and a CAN bus controller such as SJA1000, such as a main form MCP2510. Perhaps this very strong function of the node However, some applications are completely unnecessary, such as thin clients CAN applications, usually do not have the number of functional nodes, only requires nodes to collect data can, at this time, MCU CAN controller seems some way on too complex and expensive; However, if a device MCP25050 CAN bus extension to form, then not only simplify the system design can also reduce design costs, because this program requires only a MCP25050 and a CAN bus can drive it without MCU and CAN bus controller. the common circuit shown in Figure 3.
Application MCP25050 CAN bus node expansion is a convenient and economical way. In existing or new CAN bus system will bring a lot of convenience to use it, its big advantage is that without MCU. The author in the design of multi-point temperature monitoring CAN system successfully used in the program. proved, MCP25050 high reliability and stable operation.