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Inter-IC Bus

Inter-IC Bus. 2. (I C). SCI 1. SCI 1. ATD 1. ATD 0. 12K SRAM. 256K FLASEEPROM. Internal Bus. SPI 2 or PWM CH 4-7. SPI 1 or PWM CH 0-3. SPI 0. BKP INT MMI. PWM 8 CHAN. HCS12 CPU. SIM. CM BDM MEBI. PLL PIT. msCAN

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Inter-IC Bus

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  1. Inter-IC Bus 2 (I C)

  2. SCI 1 SCI 1 ATD 1 ATD 0 12K SRAM 256K FLASEEPROM Internal Bus SPI 2 or PWM CH 4-7 SPI 1 or PWM CH 0-3 SPI 0 BKP INT MMI PWM 8 CHAN HCS12 CPU SIM CM BDM MEBI PLL PIT msCAN 4 or IIC msCAN 3 msCAN 2 msCAN 1 BDLC or msCAN 0 ECT 8 CHAN 4K BYTES EEPROM

  3. IIC Features • • Compatible with I2C Bus standard • • Multi-master operation • • Software programmable for one of 256 different serial clock frequencies • • Software selectable acknowledge bit • • Interrupt driven byte-by-byte data transfer • • Arbitration lost interrupt with automatic mode switching from • master to slave • • Calling address identification interrupt • • Start and stop signal generation/detection • • Repeated start signal generation • • Acknowledge bit generation/detection • • Bus busy detection • Low power modes support • Shared with msCAN 4

  4. IIC Functional Block Diagram Address Module IIC_Interrupt R_Data W_Data SCL D_IN IN/OUT D_OUT

  5. IIC Communication Protocol START signal is defined as a high-to-low transition of SDA while SCL is high. A master may initiate communication by sending a START signal. This signal denotes the beginning of a new data transfer (each data transfer may contain several bytes of data) and brings all slaves out of their idle states. Slave Address: An address byte followed by 1-bit R/W command to tell the Slave the desired direction of data transfer. ACK Bit - Slave Transfer Acknowledge. Stop: Master generates a Stop signal to free the bus. Repeat Start: Repeat Start is a Start signal without generating a Stop signal to terminate communication.

  6. IIC Registers IBAD - IIC Address Register Address Offset $0000 ADR[7:1] - Slave Address Address of selected IIC slave device IBDR - IIC Data I/O Register Bit 7 6 5 4 3 2 1 Bit 0 $0004 IIC Master initiates data transmission by writing data to this register. IIC Master initiates data reception of next byte by reading this register.

  7. IIC Registers IBFR - IIC Frequency Divider Register Address Offset $0001 Bit 7 6 5 4 3 2 1 Bit 0 I-Bus Tap and Prescale Values I-Bus Tap and Prescale Values Division Factor IBC[2:0] SCL Tap SDA Tap Clocks Clocks 000 5 1 001 6 1 010 7 2 011 8 2 100 9 3 101 10 3 110 12 4 111 15 4 IBC[5:3] SCL2Tap Tap2Tap (Bin) (Clocks) (Clocks) 000 5 1 001 6 2 010 6 4 011 6 8 100 6 16 101 14 32 110 30 64 111 126 128 IBC[7:6] DIV 00 1 01 2 10 4 11 Reserved SCL Divider = DIV x {2 scl2tap + [(SCL_Tap -1 ) x tap2tap ] +2)} SCL Hold = DIV x {scl2tap + [(SCL_Tap -1) x tap2tap] +3 }

  8. I-Bus Transfer Control IBCR - IIC Control Register Address Offset $0002 Bit 7 6 5 4 3 2 1 Bit 0 IBEN — I-Bus Enable This bit controls the software reset of the entire IIC Bus module. 1 = The IIC Bus module is enabled. This bit must be set before any other IBCR bits have any effect. 0 = The module is reset and disabled. IBIE - I-Bus Interrupt Enable 1 = IIC Interrupts Enabled MS/SL - Master/Slave Mode Select A change from “0’ to “1” enables IIC as Master and causes a Start Signal generation. A change from “1’ to “0” changes IIC from Master to Slave & causes a Stop Signal generation. Tx/Rx - Transmit/Receive Mode Select Selects direction of data transfer. The Master should set this bit during address transfer cycle. 1 = Transmit Mode 0 = Receive Mode TXAK - Transmit Acknowledge Enable 1 = No Acknowledge response is sent 0 = Acknowledge signal will be sent on the 9th clock bit RSTA - Repeat Start The master generates a Repeat Star signal on the IIC bus by writing this bit with a logic”1”. IBSWAI - I_Bus Interface Stop in Wait Mode 1 = Will cause the IIC Bus to Halt when the CPU executes wait instruction. 0 = IIC Bus continues to run normally in wait mode

  9. I-Bus Status Bit 7 6 5 4 3 2 1 Bit 0 TCF - Data Transfer Bit 1 = Transfer is complete. This bit is set on 9th clock of a byte transfer. 0 = Transfer in progress. IAAS - Addressed as a Slave This bit is set when the calling address matches the I-Bus Address Register 1 = Addressed as a slave and an interrupt is requested if enabled. 0 = Not addressed To clear this bit, a write to I-Bus Control Register. IBB - I-Bus Busy This bit is set when a Start signal is detected. It is cleared when I-Bus is idle. IBAL - Arbitration Lost This bit is set for the following conditions: 1. SDA sampled as a low when the master drives a high during an address or data transmit cycle. 2. SDA sampled as a low when the master drives a high during the acknowledge bit of a data receive cycle. 3. A start cycle is attempted when the bus is busy. 4. A repeated start cycle is requested in slave mode. 5. A stop condition is detected when the master did not request it. (This bit must be cleared by software, by writing a “0” to it.) SRW - Slave Read/Write When the I-Bus is selected as a Slave, this bit indicates the R/W command bit of the calling address sent from the Master. 1 = Slave transmit, Master reading from Slave. 0 = Slave receive, Master writing to Slave. IBIF - I-Bus Interrupt I-Bus generates an interrupt request for the following events: 1. Completion of one byte transfer. 2. Reception of a matching calling address. 3. When arbitration is lost. (To clear this bit, write a “0” to it in the interrupt service routine) RXAK - Receive Acknowledge 1 = No Acknowledge signal is detected on 9th bit clock. 0 = Acknowledge signal was detected on 9th bit clock.

  10. Initialization Initialization Sequence: Reset will put the IIC Control Register to its default status. Before the interface can be used to transfer serial data, an initialization procedure must be carried out, as follows: 1. Update the Frequency Divider Register (IBFD) and select the required division ratio to obtain SCL frequency from system clock. 2. Update the IIC Address Register (IBAD) to define its slave address. 3. Set the IBEN bit of the IIC Control Register (IBCR) to enable the IIC system. 4. Modify the bits of the IIC Control Register (IBCR) to select Master/Slave mode, Transmit/Receive mode and interrupt enable or not.

  11. Start Bit Generation Sequence An example of a program which generates the START signal and transmits the first byte of data (slave address) is shown below: CHFLAG BRSET IBSR,#$20 ;WAIT FOR IBB FLAG TO CLEAR TXSTART BSET IBCR,#$30 ;SET TRANSMIT AND MASTER MODE ;i.e. GENERATE START CONDITION MOVEB CALLING,IBDR ;TRANSMIT THE CALLING ;ADDRESS, D0=R/W IBFREE BRCLR #5,IBSR,#$20 ;WAIT FOR IBB FLAG TO SET Stop Bit Generation Sequence A data transfer ends with a STOP signal generated by the ‘master.’ The following is an example showing how a stop condition is generated. MASTX TST TXCNT ;TEST VALUE OF TRANSMITING COUNTER BEQ END ;END IF NO MORE DATA BRSET IBSR,#$01,END ;END IF NO ACK MOVB DATABUF,IBDR ;TRANSMIT NEXT BYTE OF DATA DEC TXCNT ;DECREASE THE TXCNT BRA EMASTX ;EXIT END BCLR IBCR,#$20 ;GENERATE A STOP CONDITION EMASTX RTI ;RETURN FROM INTERRUPT

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