HG24C256C
http://www.hgsemi.com.cn 2016 DEC
Device Communication
The HG24C256C operates as a slave device and utilizes a 2-wire serial interface to communicate with the Master. The Master
initiates and controls all Read and Write operations to the slave devices on the serialbus, and both the Master and the slave
devices can transmit and receive data on the bus.
The serial interface is comprised of just two signal lines: the Serial Clock (SCL) and the Serial Data (SDA). Data is always
latched into the HG24C256C on the rising edge of SCL and is always output from the deviceon the falling edge of SCL. Both
the SCL pin and SDA pin incorporate integrated spike suppression filtersand Schmitt Triggers to minimize the effects of input
spikes and bus noise.
All command and data information is transferred with the Most Significant Bit (MSB) first. During the bus communication, one
data bit is transmitted every clock cycle, and after eight bits of data has been transferred, the receiving device must respond
with an acknowledge or a no-acknowledge response bit during a ninth clock cycle generated by the Master. Therefore, nine
clock cycles are required for every one byte of data transferred. There is no unused clock cycle during any Read or Write
operation, so theremust not be any interruptions or breaks during the data stream.
During data transfers, data on the SDA pin must only change while SCL is low, and the data must remainstable while SCL is
high. If data on the SDA pin changes while SCL is high, then either a Start or a Stop condition will occur. The number of data
bytes transferred between a Start and a Stop condition is not limited and is determined by the Master.
Start Condition
A Start condition occurs when there is a high-to-low transition on the SDA pin while the SCL pin is stable in Logic 1 state. The
Start condition must precede any command as the Master uses a Start condition to initiate any data transfer sequence (see
Figure 1). The HG24C256C will continuously monitor the SDA and SCL pins for a Start condition, and the device will not
respond unless one is given.
Figure 1 Start, Stop, and ACK
Stop Condition
A Stop condition occurs when there is a low-to-high transition on the SDA pin while the SCL pin is stable inLogic 1 state (see
Figure 1). A stop condition terminates communication between the HG24C256C and the Master. A Stop condition at the end of
a Write command triggers the EEPROM internal write cycle. Otherwise, the HG24C256C subsequently returns to Standby
mode after receiving a Stop condition.
Acknowledge (ACK)
After each byte of data is received, the HG24C256C should acknowledge to the Master that it has received the data byte
successfully. This is accomplished by the Master first releasing the SDA line and providing the ACK/NACK clock cycle (a ninth
clock cycle for every byte). During the ACK/NACK clock cycle, the HG24C256C must output Logic 0 as ACK for the entire clock
cycle so that the SDA line must be stable in Logic 0 state during the entire high period of the clock cycle (see Figure 1).