MAX127 Data Sheet help me understand what they mean 9th bit ACK
sam_sam_sam
Posts: 2,286
Here is the data sheet http://datasheets.maxim-ic.com/en/ds/MAX127-MAX128B.pdf
Read a Conversion (Read Cycle)
Once a conversion starts, the master does not need to wait for the conversion to end before attempting to read the data from the slave. Data access begins with the master issuing a START condition followed by a 7-bit address (Figure 3) and a read bit (R/W = 1). Once the eighth bit has been received and the address matches,the slave issues an acknowledge by pulling low on SDA for one clock cycle (A = 0) followed by the·first byte ofserial data (D11D4, MSB first). After the first byte has been issued by the slave, it releases the bus for themaster to issue an acknowledge (A = 0). After receiving the acknowledge, the slave issues the second byte (D3D0 and four zeros) followed by a NOT acknowledge (A=1) from the master to indicate that the last data byte has been received. Finally, the master issues a STOP condition (P), ending the read cycle (Figure 7).
(Figure 7).
|_ START _| |_ SEL2 _| |_ SEL1 _| |_ SEL0 _| |_ RNG _| |_ BIP _| |_ PD1_| |_ PD0 _| |_ ACK_|
MSB········································································································ ·LSB
SCL |___|````|___|````|___|````|___|````|___|````|___|````|___|````|___|````|___|````·
START: FIRST LOGIC "1" RECEIVED AFTER ACKNOWLEDGE OF A WRITE.
Please explain what this mean and how would you write the command to do this
ACK: ACKNOWLEDGE BIT. THE MAX127/MAX128 PULL SDA LOW DURING THE 9TH CLOCK PULSE.
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··Thanks for any·
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Sam
Post Edited (sam_sam_sam) : 12/6/2009 1:45:50 AM GMT
Comments
This just an extra form of handshaking with the I2C protocol. Sometimes it is used and sometimes not. Basically after you send data to the MAX127/MAX128, it will pull the SDA LOW if the data that you just sent was received properly. Usually the I2C Master goes on blind assumptions that the data was received correctly and does not look at the ACK. In some cases it is required, but in others it can simply be ignored. If you want to implement this extra bit of handshaking, then you simply look for the valid ACK state after you have sent your data.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.