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M38023E8-XXXFS Datasheet(PDF) 53 Page - Renesas Technology Corp |
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M38023E8-XXXFS Datasheet(HTML) 53 Page - Renesas Technology Corp |
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53 / 208 page  1-37 HARDWARE 3802 GROUP USER’S MANUAL NOTES ON PROGRAMMING Processor Status Register The contents of the processor status register (PS) after a reset are undefined, except for the interrupt disable flag (I) which is “1”. Af- ter a reset, initialize flags which affect program execution. In particular, it is essential to initialize the index X mode (T) and the decimal mode (D) flags because of their effect on calculations. Interrupts The contents of the interrupt request bits do not change immedi- ately after they have been written. After writing to an interrupt re- quest register, execute at least one instruction before executing a BBC or BBS instruction. Decimal Calculations To calculate in decimal notation, set the decimal mode flag (D) to “1”, then execute an ADC or SBC instruction. Only the ADC and SBC instructions yield proper decimal results. After executing an ADC or SBC instruction, execute at least one instruction before executing a SEC, CLC, or CLD instruction. In decimal mode, the values of the negative (N), overflow (V), and zero (Z) flags are invalid. The carry flag can be used to indicate whether a carry or borrow has occurred. Initialize the carry flag before each calculation. Clear the carry flag before an ADC and set the flag before an SBC. Timers If a value n (between 0 and 255) is written to a timer latch, the fre- quency division ratio is 1/(n + 1). Multiplication and Division Instructions The index X mode (T) and the decimal mode (D) flags do not af- fect the MUL and DIV instruction. The execution of these instructions does not change the contents of the processor status register. Ports The contents of the port direction registers cannot be read. The following cannot be used: • The data transfer instruction (LDA, etc.) • The operation instruction when the index X mode flag (T) is “1” • The addressing mode which uses the value of a direction regis- ter as an index • The bit-test instruction (BBC or BBS, etc.) to a direction register • The read-modify-write instruction (ROR, CLB, or SEB, etc.) to a direction register Use instructions such as LDM and STA, etc., to set the port direc- tion registers. Serial I/O In clock synchronous serial I/O, if the receive side is using an ex- ternal clock and it is to output the SRDY1 signal, set the transmit enable bit, the receive enable bit, and the SRDY1 output enable bit to “1”. Serial I/O1 continues to output the final bit from the TXD pin after transmission is completed. The SOUT2 pin from serial I/O2 goes to high impedance after transmission is completed. A-D Converter The comparator uses internal capacitors whose charge will be lost if the clock frequency is too low. Make sure that f(XIN) is at least 500 kHz during an A-D conver- sion. (If the ONW pin has been set to “L”, the A-D conversion will take twice as long to match the longer bus cycle, and so f(XIN) must be at least 1 MHz.) Do not execute the STP or WIT instruction during an A-D conver- sion. D-A Converter The accuracy of the D-A converter becomes poor rapidly under the VCC = 3.0 V or less condition. Instruction Execution Time The instruction execution time is obtained by multiplying the fre- quency of the internal clock φ by the number of cycles needed to execute an instruction. The number of cycles required to execute an instruction is shown in the list of machine instructions. The frequency of the internal clock φ is half of the XIN frequency. When the ONW function is used in modes other than single-chip mode, the frequency of the internal clock φ may be one fourth the XIN frequency. Memory Expansion Mode The memory expansion mode is not available in the following mi- crocomputers. • M38024M6-XXXSP • M38024M6-XXXFP Memory Expansion Mode and Microproces- sor Mode Execute the LDM or STA instruction for writing to port P3 (address 000616) in memory expansion mode and microprocessor mode. Set areas which can be read out and write to port P3 (address 000616) in a memory, using the read-modify-write instruction (SEB, CLB). NOTE ON PROGRAMMING |
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