5.3

10

IDT79R3051/79R3052 INTEGRATED RISControllers

COMMERCIAL TEMPERATURE RANGE

PIN DESCRIPTION (Continued):

PIN NAME

I/O

DESCRIPTION

Burst/

O

Burst Transfer/Write Near: On read transactions, the

Burst signal indicates that the current bus read

WrNear

is requesting a block of four contiguous words from memory. This signal is asserted only in read cycles

due to cache misses; it is asserted for all I-Cache miss read cycles, and for D-Cache miss read cycles

if selected at device reset time.

On write transactions, the

WrNear output tells the external memory system that the bus interface unit

is performing back-to-back write transactions to an address within the same 256 word page as the prior

write transaction. This signal is useful in memory systems which employ page mode or static column

DRAMs, and allows near writes to be retired quickly.

Rd

O

Read: An output which indicates that the current bus transaction is a read.

Wr

O

Write: An output which indicates that the current bus transaction is a write.

Ack

I

Acknowledge: An input which indicates to the device that the memory system has sufficiently

processed the bus transaction, and that the CPU may either terminate the write cycle or process the read

data from this read transfer.

RdCEn

I

Read Buffer Clock Enable: An input which indicates to the device that the memory system has placed

valid data on the A/D bus, and that the processor may move the data into the on-chip Read Buffer.

SysClk

O

System Reference Clock: An output from the CPU which reflects the timing of the internal processor

"Sys" clock. This clock is used to control state transitions in the read buffer, write buffer, memory

controller, and bus interface unit.

BusReq

I

DMA Arbiter Bus Request: An input to the device which requests that the CPU tri-state its bus interface

signals so that they may be driven by an external master.

BusGnt

O

DMA Arbiter Bus Grant. An output from the CPU used to acknowledge that a

BusReq has been

detected, and that the bus is relinquished to the external master.

SBrCond(3:2)

I

Branch Condition Port: These external signals are internally connected to the CPU signals

BrCond(1:0)

CpCond(3:0). These signals can be used by the branch on co-processor condition instructions as input

ports. There are two types of Branch Condition inputs: the SBrCond inputs have special internal logic

to synchronize the inputs, and thus may be driven by asynchronous agents. The direct Branch Condition

inputs must be driven synchronously.

BErr

I

Bus Error: Input to the bus interface unit to terminate a bus transaction due to an external bus error.

This signal is only sampled during read and write operations. If the bus transaction is a read operation,

then the CPU will take a bus error exception.

Int(5:3)

I

Processor Interrupt: During normal operation, these signals are logically the same as the

Int(5:0)

SInt(2:0)

signals of the R3000. During processor reset, these signals perform mode initialization of the CPU, but

in a different (simpler) fashion than the interrupt signals of the R3000.

There are two types of interrupt inputs: the

SInt inputs are internally synchronized by the processor, and

may be driven by an asynchronous external agent. The direct interrupt inputs are not internally

synchronized, and thus must be externally synchronized to the CPU. The direct interrupt inputs have

one cycle lower latency than the synchronized interrupts.

Clk2xIn

I

Master Clock Input: This is a double frequency input used to control the timing of the CPU.

Reset

I

Master Processor Reset: This signal initializes the CPU. Mode selection is performed during the last

cycle of

Reset.

Rsvd(4:0)

I/O

Reserved: These five signal pins are reserved for testing and for future revisions of this device. Users

must not connect these pins.

2874 tbl 03