MC68340 datasheet(361/441 Pages) FREESCALE

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MOTOROLA

MC68340 USER’S MANUAL

8- 17

Table 8-1. OCx Encoding

OC1

OC0

TOUTx

Hi-Z

A read of the SR while in this mode always shows the TO, TC, and COM bits cleared, and

the PO bits as $FF. The SR OUT bit always indicates the level on the TOUTx pin.

8.3.9 Bus Operation

The following paragraphs describe the operation of the IMB during read, write, and

interrupt acknowledge cycles to the timer.

8.3.9.1 READ CYCLES. The timer is accessed with no wait states. The timer responds to

byte, word, and long-word reads, and 16 bits of valid data are returned. Read cycles from

reserved registers return logic zero.

8.3.9.2 WRITE CYCLES. The timer is accessed with no wait states. The timer responds to

byte, word, and long-word writes. Write cycles to read-only registers and bits as well as

reserved registers complete in a normal manner without exception processing; however,

the data is ignored.

8.3.9.3 INTERRUPT ACKNOWLEDGE CYCLES. The timer is capable of arbitrating for

interrupt servicing and supplying the interrupt vector when it has successfully won

arbitration. The vector number must be provided if interrupt servicing is necessary; thus,

the interrupt register (IR) must be initialized. If the IR is not initialized, a spurious interrupt

exception will be taken if interrupt servicing is necessary.

8.4 REGISTER DESCRIPTION

The following paragraphs contain a detailed description of each register and its specific

function. The operation of the timer is controlled by writing control words into the

appropriate registers. Timer registers and their associated addresses are listed in Figure

8-11. For more information about a particular register, refer to the individual register

description. The ADDR column indicates the offset of the register from the base address

of the timer. An FC column designation of S indicates that register access is restricted to

supervisor only. A designation of S/U indicates that access is governed by the SUPV bit in

the module configuration register (MCR).

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MC68340 Datasheet(PDF) 361 Page - Freescale Semiconductor, Inc