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MT9M114 Fiches technique(PDF) 34 Page - ON Semiconductor |
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MT9M114 Fiches technique(HTML) 34 Page - ON Semiconductor |
34 / 45 page MT9M114 www.onsemi.com 34 HARDWARE FUNCTIONS Two-Wire Serial Interface The two-wire serial interface bus enables read and write access to control and status registers and variables within the MT9M114. The interface protocol uses a master/slave model in which a master controls one or more slave devices. The MT9M114 always operates in slave mode. The host (master) generates a clock (SCLK) that is an input to the MT9M114 and is used to synchronize transfers. Data is transferred between the master and the slave on a bidirectional signal (SDATA). The host should always ensure that the following relationship is adhered to. S CLK v PIXEL CLOCK 22 Protocol Data transfers on the two-wire serial interface bus are performed by a sequence of low-level protocol elements, as follows: 1. a (repeated) start condition 2. a slave address/data direction byte 3. a 16-bit register address (8-bit addresses are not supported) 4. an (a no) acknowledge bit 5. a 16-bit data transfer (8-bit data transfers are not supported) 6. a stop condition The bus is idle when both SCLK and SDATA are HIGH. Control of the bus is initiated with a start condition, and the bus is released with a stop condition. Only the master can generate the start and stop conditions. A start condition is defined as a HIGH-to-LOW transition on SDATA while SCLK is HIGH. At the end of a transfer, the master can generate a start condition without previously generating a stop condition; this is known as a repeated start or restart condition. A stop condition is defined as a LOW-to-HIGH transition on SDATA while SCLK is HIGH. Data is transferred serially, 8 bits at a time, with the most significant bit (MSB) transmitted first. Each byte of data is followed by an acknowledge bit or a no-acknowledge bit. This data transfer mechanism is used for the slave address/data direction byte and for message bytes. One data bit is transferred during each SCLK clock period. SDATA can change when SCLK is LOW and must be stable while SCLK is HIGH. Slave Address Bits [7:1] of this byte represent the device slave address and bit [0] indicates the data transfer direction. A “0” in bit [0] indicates a WRITE, and a “1” indicates a READ. If the SADDR signal is driven LOW, then addresses used by the MT9M114 are R0x090 (write address) and R0x091 (read address). If the SADDR signal is driven HIGH, then addresses used by the MT9M114 are R0x0BA (write address) and R0x0BB (read address). Message Byte Message bytes are used for sending register addresses and register write data to the slave device and for retrieving register read data. The protocol used is outside the scope of the two-wire serial interface specification. Acknowledge Bit Each 8-bit data transfer is followed by an acknowledge bit or a no-acknowledge bit in the SCLK clock period following the data transfer. The transmitter (which is the master when writing, or the slave when reading) releases SDATA. The receiver indicates an acknowledge bit by driving SDATA LOW. As for data transfers, SDATA can change when SCLK is LOW and must be stable while SCLK is HIGH. No-Acknowledge Bit The no-acknowledge bit is generated when the receiver does not drive SDATA low during the SCLK clock period following a data transfer. A no-acknowledge bit is used to terminate a read sequence. Stop Condition A stop condition is defined as a LOW-to-HIGH transition on SDATA while SCLK is HIGH. Typical Serial Transfer A typical read or write sequence begins by the master generating a start condition on the bus. After the start condition, the master sends the 8-bit slave address/data direction byte. The last bit indicates whether the request is for a read or a write, where a “0” indicates a write and a “1” indicates a read. If the address matches the address of the slave device, the slave device acknowledges receipt of the address by generating an acknowledge bit on the bus. If the request was a write, the master then transfers the 16-bit register address to which a write should take place. This transfer takes place as two 8-bit sequences and the slave sends an acknowledge bit after each sequence to indicate that the byte has been received. The master then transfers the data as an 8-bit sequence; the slave sends acknowledge bit at the end of the sequence. After 8 bits have been transferred, the slave’s internal register address is automatically incremented, so that the next 8 bits are written to the next register address. The master stops writing by generating a (re)start or stop condition. If the request was a read, the master sends the 8-bit write slave address/data direction byte and 16-bit register address, just as in the write request. The master then generates a (re)start condition and the 8-bit read slave address/data direction byte, and clocks out the register data, 8 bits at a time. The master generates an acknowledge bit after each 8-bit transfer. The slave’s internal register address is automatically incremented after every 8 bits are transferred. The data transfer is stopped when the master sends a no-acknowledge bit. |
Numéro de pièce similaire - MT9M114_1 |
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Description similaire - MT9M114_1 |
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