Receiving Messages, Receive Byte, CPU Jrxbuf | Intel 8XC196Lx

J1850 COMMUNICATIONS CONTROLLER

NOTE

An overrun condition can occur on transmission if the transmit buffer,

JTX_BUF, is overwritten.

8.5.2Receiving Messages

For a message reception, after a SOF is detected on the bus, the controller starts to shift data sym- bols into the J1850 receive buffer (JRX_BUF) until an entire data byte has been received. This byte is automatically transferred into the J1850 receive (J_RX) register (Figure 8-14) and the sub- sequent byte is written into the empty JRX_BUF.

J_RX	Address:	1F52H
	Reset State:	00H

The J1850 receiver (J_RX) register transfers received data in byte increments from the J1850 bus to the microcontroller CPU. This register is buffered to allow for reception of a second data byte while the first data byte is being read. This byte register can be read or written, and is addressable through windowing.

	7		0
			Receive Byte

	Bit	Bit	Function
	Number	Mnemonic	Function
	Number	Mnemonic

	7:0	DB7:0	Data Bits
			These eight bits compose the last data byte received from the J1850 bus.

Figure 8-14. J1850 Receiver (J_RX) Register

The transfer of the first byte to J_RX triggers the reception process and generates the J1850 re- ception (J1850RX) interrupt (if it is enabled), signaling that JRX_BUF is available for another byte (Figure 8-15).

CPU

JRX_BUF		J1850 Bus

Message receive interrupt (J1850RX) set

J_RX

A5236-01

Figure 8-15. J1850 Receive Message Structure

After J_RX is read, the byte residing in JRX_BUF is automatically shifted into J_RX, freeing JRX_BUF for another reception. This process continues until an end of data (EOD) symbol is en- countered.

8-15

Image 81

Intel 8XC196Lx, 8XC196Jx, 8XC196Kx, 87C196CA user manual Receiving Messages, Receive Byte, CPU Jrxbuf

Contents

August Page Contents 8XC196LX Supplement Chapter Synchronous Serial I/O Port Functional Groupings of Signals Default Conditions Entering and Exiting Once ModeProgramming the J1850 Controller Internal Timing Figures 11-3 Tables Guide to This Manual Page Chapter Guide to this Manual Manual Contents Related Documents Related Documents Architectural Overview Page Microcontroller Features Features of the 8XC196Lx and 8XC196Kx Product FamiiesChapter Architectural Overview Internal Timing Block Diagram Clock Circuitry 87C196LA, LB Only MHz State Times at Various Frequencies12 MHz 16 MHz External Timing PllenMultiplier State Time Internal Peripherals Uprom Programming Values and LocationsCLK1 CLK0 Synchronous Serial I/O Port 1 I/O PortsEvent Processor Array 4 J1850 Communications ControllerPage Address Space Page Chapter Address Space Address PartitionsAddress Map 1BFF Register File Address CA,JT,KTJR, KR Peripheral SPECIAL-FUNCTION Registers XC196Lx Peripheral SFRsUSFR1 LA, LB SSIO0CLK SSIO1CLKRstsrc Jdly Windows Windowing Base Upper Register File CA, JT, JV, KTUpper Register File CA, JT, JV, KT, LA, LB 4BH 0140H25H 0120H 49H 0100H 48H 24H 12H Standard and PTS Interrupts Page Interrupt SOURCES, VECTORS, and Priorities Chapter Standard and PTS Interrupts Interrupt Registers Interrupt Controller PTS ServiceInterrupt Sources, Vectors, and Priorities Interrupt Source Mnemonic Priority Name Intmask Interrupt Mask RegistersBit Function Number Bit Mnemonic Interrupt Description INTMASK1 Interrupt Pending RegistersLA, LD NMI Extint SSIO1 SSIO0 Intpend Interrupt Pending Intpend Register Peripheral Transaction Server Registers INTPEND1NMI Ptssel BitInterrupt PTS Vector Ptssrv BitsInterrupt Standard Vector Ports Page I/O Ports Overview Chapter PortsMicrocontroller Ports EPA, Ssio 8XC196LX Supplement Ports 1, 2, 5, and 6 Internal Structure 87C196LA, LB Only Configuring Ports 1, 2, 5, and 6 Bidirectional Ports Special Bidirectional Port Considerations For complementary output configurations Internal Structure for Ports 3 and 4 ADDRESS/DATA BUS 8XC196L X Supplement Synchronous Serial Port Page Ssio 0 Clock Register Chapter Synchronous Serial I/O PortBit Function For receptions 1FB7H Ssio 1 Clock RegisterCHS DUP Conint Conpnd Phas Pols CHS SSIO1CLK Page Event Processor Array Page EPA Functional Overview Chapter Event Processor ArrayEPA Channels Device Capture/Compare Compare-only EPA Block Diagram 87C196LA, LB Only EPA Block Diagram 83C196LD Only EPA Mask Registers EpamaskEPAMASK1 EPA Pending Registers EpapendEPAPEND1 EPA Interrupt Priority Vector Register Value InterruptEpaipv J1850 Communications Controller Page J1850 Communications Controller J1850 Functional OverviewPLL Clkout J1850 Communications Controller Block Diagram J1850 Controller Signals J1850 Controller Signals and RegistersSignal Control and Status Registers J1850 Controller Operation Control State MachineCyclic Redundancy Check Generator Bus Contention Symbol Synchronization and Timing CircuitryError Detection Bit Arbitration Symbol Encoding and Decoding Delay CompensationClock Prescaler Digital Filter Bit Arbitration Example Huntzicker Symbol Definition for J1850 Bit Arbitration Example Message Frames Header Standard MessagingCRC Byte Normalization Bit 64µS 128µS NB for IFR with CRC NB for IFR without CRC Name Symbol Bus Level TXmin TXnom TXmax RXmin RXmax Units Huntzicker Symbol Timing Characteristics IFR Messaging Type 1 Single Byte, Single Responder In-frame Response Messaging Transmitting Messages Transmitting and Receiving Messages CPU JTX Jtxbuf Transmit Byte Receiving Messages Receive ByteCPU Jrxbuf Programming the J1850 Command Jcmd Register IFR MessagesProgramming the J1850 Controller Auto IFR Ignore Abort MSG3 MSG2 MSG1 MSG0 JcmdAuto MSG30 Operation Purpose NBF IFR3 4XM Txbrk Rxpol PRE1 PRE0 Programming the J1850 Configuration Jcfg RegisterNBF IFR without CRC Byte PRE1 PRE0 Programming the J1850 Delay Compensation Jdly Register 18. J1850 Delay Jdly Register Jstat Programming the J1850 Status Jstat Register Msgrx Msgtx Minimum Hardware Considerations Page Minimum Hardware Considerations Identifying the Reset Source Design Considerations for 8XC196LA, LB, and LD Special Operating Modes Page Chapter Special Operating Modes Entering and Exiting Once Mode 10-3 Page Programming Nonvolatile Memory Page Signature Word and Programming Voltage Values Programming the Nonvolatile MemoryOtprom Address MAP Signature Word and Programming Voltage Values C196LA, LB Otprom Address Map Slave Programming Circuit and Address MAPAddress Range Description Hex CCB1 Description Address Comments Serial Port Programming Circuit Serial Port Programming Circuit and Address MAP Description Address Range Serial Port Programming Mode Address MapA000-FFFFH Do not addressPage Signal Descriptions Page Functional Groupings of Signals Appendix a Signal Descriptions Table A-1 C196LA Signals Arranged by Functional Categories Signal Descriptions Table A-2 C196LB Signals Arranged by Functional Categories Figure A-2 C196LB 52-pin Plcc Package Input Name Pin Table A-3 C196LD Signals Arranged by Functional CategoriesInput/Output Cont’d Name Pin Bus Control & Status Default Conditions Table A-5 C196LA, LB Default Signal Conditions Port Alternate During RESET# Upon RESET# PowerSignals Functions Table A-6 C196LD Default Signal Conditions Page Glossary Page Glossary ALUBIT Byte DOUBLE-WORD EPAESD Integer FET LONG-INTEGER ISRLSB LSW MSW MSB PIC PIH PLL PSW PTSPtscb Ralu QUAD-WORD SAR SFRSHORT-INTEGER Uart VPW WDTWord Index Page Clkout Index Index-2