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COP8ACC5 Datasheet(PDF) 30 Page - National Semiconductor (TI) |
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COP8ACC5 Datasheet(HTML) 30 Page - National Semiconductor (TI) |
30 / 41 page MICROWIRE/PLUS (Continued) TABLE 9. MICROWIRE/PLUS Master Mode Clock Select SL1 SL0 SK period 0 0 2Xt C 0 1 4Xt C 1 x 8Xt C Where t C is the instruction cycle clock MICROWIRE/PLUS OPERATION Setting the BUSY bit in the PSW register causes the MICROWIRE/PLUS 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. If enabled, an interrupt is generated when eight data bits have been shifted. The device may enter the MICROWIRE/PLUS mode either as a Master or as a Slave. Figure 18 shows how two devices, microcontrollers and several peripherals may be interconnected using the MICROWIRE/PLUS arrangements. WARNING The SIO register should only be loaded when the SK clock is low. Loading the SIO register while the SK clock is high will result in undefined data in the SIO register. SK clock is nor- mally low when not shifting. Setting the BUSY flag when the input SK clock is high in the MICROWIRE/PLUS slave mode may cause the current SK clock for the SIO shift register to be narrow. For safety, the BUSY flag should only be set when the input SK clock is low. MICROWIRE/PLUS Master Mode Operation In the MICROWIRE/PLUS Master mode of operation the shift clock (SK) is generated internally. The MICROWIRE Master always initiates all data exchanges. The MSEL bit in the CNTRL register must be set to enable the SO and SK functions onto the G Port. The SO and SK pins must also be selected as outputs by setting appropriate bits in the Port G configuration register. Table 10 summarizes the bit settings required for Master mode of operation. MICROWIRE/PLUS Slave Mode Operation In the MICROWIRE/PLUS Slave mode of operation the SK clock is generated by an external source. Setting the MSEL bit in the CNTRL register enables the SO and SK functions onto the G Port. The SK pin must be selected as an input and the SO pin is selected as an output pin by setting and re- setting the appropriate bits in the Port G configuration regis- ter. Table XI summarizes the settings required to enter the Slave mode of operation. The user must set the BUSY flag immediately upon entering the Slave mode. This will ensure that all data bits sent by the Master will be shifted properly. After eight clock pulses the BUSY flag will be cleared and the sequence may be re- peated. TABLE 10. MICROWIRE/PLUS Mode Settings This table assumes that the control flag MSEL is set. G4 (SO) G5 (SK) G4 G5 Operation Config. Bit Config. Bit Fun. Fun. 1 1 SO Int. MICROWIRE/PLUS SK Master 0 1 TRI- Int. MICROWIRE/PLUS STATE SK Master 1 0 SO Ext. MICROWIRE/PLUS SK Slave 0 0 TRI- Ext. MICROWIRE/PLUS STATE SK Slave Alternate SK Phase Operation The device allows either the normal SK clock or an alternate phase SK clock to shift data in and out of the SIO register. In both the modes the SK is normally low. In the normal mode data is shifted in on the rising edge of the SK clock and the data is shifted out on the falling edge of the SK clock. The SIO register is shifted on each falling edge of the SK clock. In the alternate SK phase operation, data is shifted in on the falling edge of the SK clock and shifted out on the rising edge of the SK clock. A control flag, SKSEL, allows either the normal SK clock or the alternate SK clock to be selected. Resetting SKSEL causes the MICROWIRE/PLUS logic to be clocked from the normal SK signal. Setting the SKSEL flag selects the alter- nate SK clock. The SKSEL is mapped into the G6 configura- tion bit. The SKSEL flag will power up in the reset condition, selecting the normal SK signal. DS012865-16 FIGURE 17. MICROWIRE/PLUS Block Diagram www.national.com 30 |
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