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COP87L42CJ Datasheet(PDF) 9 Page - National Semiconductor (TI) |
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COP87L42CJ Datasheet(HTML) 9 Page - National Semiconductor (TI) |
9 / 28 page Halt Mode The device is a fully static device. The device enters the HALT mode by writing a one to the G7 bit of the G data reg- ister. Once in the HALT mode, the internal circuitry does not receive any clock signal and is therefore frozen in the exact state it was in when halted. In this mode the chip will only draw leakage current. The device supports three different methods of exiting the HALT mode. The first method is with a low to high transition on the CKO (G7) pin. This method precludes the use of the crystal clock configuration (since CKO is a dedicated out- put). It may be used either with an RC clock configuration or an external clock configuration. The second method of exit- ing the HALT mode is with the multi-Input Wakeup feature on the L port. The third method of exiting the HALT mode is by pulling the RESET input low. If the two pin crystal/resonator oscillator is being used and Multi-Input Wakeup causes the device to exit the HALT mode, the WAKEUP signal does not allow the chip to start running immediately since crystal oscillators have a delayed start up time to reach full amplitude and freuqency stability. The WATCHDOG timer (consisting of an 8-bit prescaler fol- lowed by an 8-bit counter) is used to generate a fixed delay of 256tc to ensure that the oscillator has indeed stabilized before allowing instruction execution. In this case, upon de- tecting a valid WAKEUP signal only the oscillator circuitry is enabled. The WATCHDOG Counter and Prescaler are each loaded with a value of FF Hex. The WATCHDOG prescaler is clocked with the tc instruction cycle. (The tc clock is derived by dividing the oscillator clock down by a factor of 10). The Schmitt trigger following the CKI inverter on the chip en- sures that the WATCHDOG timer is clocked only when the oscillator has a sufficiently large amplitude to meet the Schmitt trigger specs. This Schmitt trigger is not part of the oscillator closed loop. The start-up timeout from the WATCH- DOG timer enables the clock signals to be routed to the rest of the chip. The delay is not activated when the device comes out of HALT mode through RESET pin. Also, if the clock option is either RC or External clock, the delay is not used, but the WATCHDOG Prescaler/-Counter contents are changed. The Development System will not emulate the 256tc delay. The RESET pin will cause the device to reset and start ex- ecuting from address X’0000. A low to high transition on the G7 pin (if single pin oscillator is used) or Multi-Input Wakeup will cause the device to start executing from the address fol- lowing the HALT instruction. When RESET pin is used to exit the device from the HALT mode and the two pin crystal/resonator (CKI/CKO) clock op- tion is selected, the contents of the Accumulator and the Timer T1 are undetermined following the reset. All other in- formation except the WATCHDOG Prescaler/Counter con- tents is retained until continuing. All information except the WATCHDOG Prescaler/Counter contents is retained if the device exits the HALT mode through G7 pin or Multi-Input Wakeup. G7 is the HALT-restart pin, but it can still be used as an input. If the device is not halted, G7 can be used as a general pur- pose input. Note: To allow clock resynchronization, it is necessary to program two NOP’s immediately after the device comes out of the HALT mode. The user must program two NOP’s following the “enter HALT mode” (set G7 data bit) instruction. MICROWIRE/PLUS MICROWIRE/PLUS is a serial synchronous bidirectional communications interface. The MICROWIRE/PLUS capabil- ity enables the device to interface with any of National Semi- conductor’s MICROWIRE peripherals (i.e. A/D converters, display drivers, EEPROMS, etc.) and with other microcon- trollers which support the MICROWIRE/PLUS interface. It consists of an 8-bit serial shift register (SIO) with serial data input (SI), serial data output (SO) and serial shift clock (SK). Figure 6 shows the block diagram of the MICROWIRE/PLUS interface. The shift clock can be selected from either an internal source or an external source. Operating the MICROWIRE/PLUS in- terface with the internal clock source is called the Master mode of operation. Operating the MICROWIRE/PLUS inter- face with an external shift clock is called the Slave mode of operation. The CNTRL register is used to configure and control the MICROWIRE/PLUS mode. To use the MICROWIRE/PLUS , the MSEL bit in the CNTRL register is set to one. The SK clock rate is selected by the two bits, SL0 and SL1, in the CNTRL register. Table 3 details the different clock rates that may be selected. TABLE 3. SL1 SL0 SK Cycle Time 00 2t c 01 4t c 1x 8t c where, t c is the instruction cycle time. MICROWIRE/PLUS OPERATION Setting the BUSY bit in the PSW register causes the MICROWIRE/PLUS arrangement to start shifting the data. It gets reset when eight data bits have been shifted. The user may reset the BUSY bit by software to allow less than 8 bits to shift. The device may enter the MICROWIRE/PLUS mode either as a Master or as a Slave. Figure 7 shows how two de- vice microcontrollers and several peripherals may be inter- connected using the MICROWIRE/PLUS arrangement. Master MICROWIRE/PLUS Operation In the MICROWIRE/PLUS Master mode of operation the shift clock (SK) is generated internally by the device. The MICROWIRE/PLUS Master always initiates all data ex- DS012529-7 FIGURE 6. MICROWIRE/PLUS Block Diagram www.national.com 9 |
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