Background Debug Mode (BDM) InterfaceMCF5253 Reference Manual, Rev. 120-6 Freescale Semiconductornext instruction needs to display captured values on DDATA, the pipeline stalls (PST = $0) until space isavailable in the FIFO.20.2.1.6 Begin Execution of RTE Instruction (PST = $7)The unique encoding is generated whenever the return-from-exception (RTE) instruction is executed.20.2.1.7 Begin Data Transfer (PST = $8–$B)These encodings serve as markers to indicate the number of bytes to be displayed on the DDATA port onsubsequent clock cycles. This encoding is driven onto the PST port one processor cycle before the actualdata is displayed on DDATA. When PST outputs a $8/$9/$A/$B marker value, the DDATA port outputs1/2/3/4 bytes of captured data respectively on consecutive processor cycles.20.2.1.8 Exception Processing (PST = $C)This encoding is displayed during normal exception processing. Exceptions which enter emulation mode(debug interrupt, or optionally trace) generate a different encoding. Because this encoding defines amulticycle mode, the PST outputs are driven with this value until exception processing is completed.20.2.1.9 Emulator Mode Exception Processing (PST = $D)This encoding is displayed during emulation mode (debug interrupt, or optionally trace). Because thisencoding defines a multicycle mode, the PST outputs are driven with this value until exception processingis completed.20.2.1.10 Processor Stopped (PST = $E)This encoding is generated as a result of the STOP instruction. The ColdFire processor remains in thestopped state until an interrupt occurs. Because this encoding defines a multicycle mode, the PST outputsare driven with this value until the stopped mode is exited.20.2.1.11 Processor Halted (PST = $F)This encoding is generated when the ColdFire processor is halted (Refer to Section 20.3.1, “CPU Halt.”)Because this encoding defines a multicycle mode, the PST outputs are driven with this value until theprocessor is restarted, or reset.20.3 Background-Debug Mode (BDM)Background debug mode (BDM) implements a low-level system debugger in the microprocessorhardware. Communication with the development system is handled through a dedicated, high-speed,full-duplex serial command interface. The BDM features are as follows:• ColdFire implements the BDM controller in a dedicated hardware module. Although some BDMoperations do require the CPU to be halted (For example, CPU register accesses), other BDMcommands such as memory accesses can be executed while the processor is running.
