M69KB128AA datasheet(28/68 Pages) STMICROELECTRONICS

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7 Configuration registers

M69KB128AA

28/68

Table 8.

7.2

Programming and Reading the Registers by the software

method

All registers (BCR, RCR, DIDR) can be read by issuing a Read Configuration Register

sequence (see Figure 8: Read Configuration Register (Software Method).

BCR and RCR can be programmed by issuing a Set Configuration Register sequence (see

Figure 7: Set Configuration Register (Software Method).

The timings will be identical to those described in Table 17: Asynchronous Read AC

Characteristics. The Configuration Register Enable input, CR, is ‘don’t care’.

Read Configuration Register and Set Configuration Register sequences both require 4 read or

write cycles. These cycles will be executed in asynchronous mode, whatever the device

operating mode:

2 bus read and one bus write cycles to a unique address location, 7FFFFFh, indicate that

the next operation will read or write to a configuration register. The data written during the

third cycle must be ‘0000h’ to access the RCR, ‘0001h’ to access the BCR and ‘0002h’ to

access the DIDR during the next cycle.

The fourth cycle reads from or writes to the configuration register.

The timings for programming and reading the registers by the software method are identical to

the asynchronous write and read timings.

Read or Write Operation

A18

A19

RCR

Read/Write

BCR

Read/Write

DIDR

Read-Only

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