MCS-51 microcontroller reads and writes USB flash drive (CH375 chip)
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CH375 is a universal interface chip for USB bus, supporting HOST mode and SLAVE mode.
The schematic diagram of the circuit for MCS-51 microcontroller to read and write USB flash disk, the TXD pin of CH375 chip is connected to high level, and it works in serial port mode. In serial port mode, CH375 only needs to connect 3 signal lines with microcontroller/DSP/MCU, TXD pin, RXD pin and INT# pin, and other pins can be left floating. Except for fewer connection lines, other peripheral circuits are basically the same as parallel port mode. Since INT# pin and TXD pin can only provide weak high-level output current during CH375 reset, when making a long-distance connection, in order to avoid INT# or TXD being disturbed during CH375 reset and causing MCU misoperation, a pull-up resistor with a resistance of 1~5kΩ can be added to INT# pin or TXD pin to maintain a relatively stable high level. After the reset of CH375 chip is completed, INT# pin and TXD pin will be able to provide 5mA high-level output current or 5mA low-level sink current.
Since CH375 has built-in firmware
for processing Mass-Storage mass storage device's dedicated communication protocol, the embedded system's microcontroller can use the USB disk (USB flash drive, USB external hard disk) as a removable large-capacity storage device through CH375. Data reading and writing only requires a few instructions, without the need to understand the USB communication protocol in detail.
If the embedded system needs to organize the USB storage device into a file system, the interface API provided by the CH375 file-level subroutine library can be called, and the subroutine library will handle the file system. The source code of the MCS-51 microcontroller reading and writing USB disk example is as follows: #include
#include "CH375INC.H"
#include /* The following definitions are applicable to MCS-51 MCU*/
#define UINT8 unsigned char
#define UINT16 unsigned short
#define UINT32 unsigned long
#define UINT8X unsigned char xdata
#define UINT8VX unsigned char volatile xdata
UINT8VX CH375_CMD_PORT _at_ 0xBDF1; /* I/O address of CH375 command port*/
UINT8VX CH375_DAT_PORT _at_ 0xBCF0; /* I/O address of CH375 data port*/
#define CH375_INT_WIRE INT0 /* P3.2, connected to INT# pin of CH375, used to query
interrupt status*/
UINT8X DISK_BUFFER[512*32] _at_ 0x0000; /* Starting address of external RAM data buffer*/ UINT32 DiskStart; /* The absolute starting sector number LBA of the logical disk */
UINT8 SecPerClus; /* The number of sectors per cluster of the logical disk */
UINT8 RsvdSecCnt; /* The number of reserved sectors of the logical disk */
UINT16 ; FATSz16; /* Number of sectors occupied by the FAT table of the FAT16 logical disk*/ /* ********** Hardware USB interface layer, this layer cannot be omitted anyway, the microcontroller must always interface with CH375*/ void mDelaymS( UINT8 delay ) {
UINT8 i, j, c;
for ( i = delay; i != 0; i -- ) {
for ( j = 200; j != 0; j -- ) c += 3;
for ( j = 200; j != 0; j -- ) c += 3;
}
} void CH375_WR_CMD_PORT( UINT8 cmd ) { /* Write command to the command port of CH375*/
CH375_CMD_PORT=cmd;
for ( cmd = 2; cmd != 0; cmd -- ); /* There should be a delay of 2uS before and after issuing the command code */
}
void CH375_WR_DAT_PORT( UINT8 dat ) { /* Write data to the data port of CH375*/
CH375_DAT_PORT=dat; /* Because the MCS51 microcontroller is slow, there is actually no need for delay*/
}
UINT8 CH375_RD_DAT_PORT( void ) { /* Read data from the data port of CH375*/
return( CH375_DAT_PORT ); /* Because the MCS51 microcontroller is slow, there is actually no need for delay*/
}
UINT8 mWaitInterrupt( void ) { /* Wait for CH375 interrupt and get status, return operation status*/
while( CH375_INT_WIRE ); /* Query and wait for CH375 operation completion interrupt (INT# low level) */
CH375_WR_CMD_PORT( CMD_GET_STATUS ); /* Generate operation completion interrupt, get interrupt status*/
return( CH375_RD_DAT_PORT() );
} /* ********** BulkOnly transmission protocol layer is built into CH375, no need to write MCU program*/ /* ********** RBC/SCSI command layer, although built into CH375, but need to write a program to issue commands and send and receive data
*/ UINT8 mInitDisk( void ) { /* Initialize disk*/
UINT8 Status;
CH375_WR_CMD_PORT( CMD_GET_STATUS ); /* Generate operation completion interrupt, get interrupt status*/
Status = CH375_RD_DAT_PORT( );
if ( Status == USB_INT_DISCONNECT ) return( Status ); /* USB device disconnected*/
CH375_WR_CMD_PORT( CMD_DISK_INIT ); /* Initialize USB storage*/
Status = mWaitInterrupt( ); /* Wait for interrupt and get status*/
if ( Status != USB_INT_SUCCESS ) return(
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