DP83916 datasheet(29/96 Pages) NSC

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40 SONIC-16 Registers (Continued)

432 Data Configuration Register

(RAk50l e 1h)

This register

(Figure 4-5) establishes the bus cycle options for readingwriting data tofrom 16- or 32-bit memory systems

During a hardware reset bits 15 and 13 are cleared all other bits are unaffected (Because of this the first thing the driver

software does to the SONIC-16 should be to set up this register) All bits are unaffected by a software reset This register must

only be accessed when the SONIC-16 is in reset mode (ie the RST bit is set in the Command register)

9876543210

EXBUS

LBR

PO1

PO0

SBUS USR1 USR0 WC1

WC0

BMS

RFT1 RFT0 TFT1 TFT0

rwereadwrite

FIGURE 4-5 Data Configuration Register

Field

Meaning

EXBUS

EXTENDED BUS MODE

LBR

LATCHED BUS RETRY

PO0PO1

PROGRAMMABLE OUTPUTS

SBUS

SYNCHRONOUS BUS MODE

USR0 USR1

USER DEFINABLE PINS

WC0 WC1

WAIT STATE CONTROL

DATA WIDTH SELECT

BMS

BLOCK MODE SELECT FOR DMA

RFT0 RFT1

RECEIVE FIFO THRESHOLD

TFT0 TFT1

TRANSMIT FIFO THRESHOLD

Bit

Description

EXBUS EXTENDED BUS MODE

Setting this bit enables the Extended Bus mode which enables the following

1) Extended Programmable Outputs EXUSR k30l This changes the TXD LBK RXC and RXD pins from the

external ENDEC interface into four programmable user outputs EXUSR k30l respectively which are similar to

USR k10l These outputs are programed with bits 15-12 in the DCR2 (see Section 437) On hardware reset

these four pins will be TRI-STATE and will remain that way until the DCR is changed If EXBUS is enabled then

these pins will remain TRI-STATE until the SONIC-16 becomes a bus master at which time they will be driven

according to the DCR2 If EXBUS is disabled then these four pins work normally as external ENDEC interface pins

2) Synchronous Termination STERM This changes the TXC pin from the External ENDEC interface into a

synchronous memory termination input for compatibility with Motorola style processors This input is only useful

when Asynchronous Bus mode is selected (bit 10 below is set to ‘‘0’’) and BMODE e 1 (Motorola mode) On

hardware reset this pin will be TRI-STATE and will remain that way until the DCR is changed If EXBUS is enabled

this pin will remain TRI-STATE until the SONIC-16 becomes a bus master at which time it will become the STERM

input If EXBUS is disabled then this pin works normally as the TXC pin for the external ENDEC interface

3) Asynchronous Bus Retry Causes BRT to be clocked in asynchronously off the falling edge of bus clock This only

applies however when the SONIC-16 is operating in asynchronous mode (bit 10 below is set to ‘‘0’’) If EXBUS is

not set BRT is sampled synchronously off the rising edge of bus clock (See Section 546)

Must be 0

LBR LATCHED BUS RETRY

The LBR bit controls the mode of operation of the BRT signal (see pin description) It allows the BUS Retry operation

to be latched or unlatched

0 Unlatched mode The assertion of BRT forces the SONIC-16 to finish the current DMA operation and get off the bus

The SONIC-16 will retry the operation when BRT is deserted

1 Latched mode The assertion of BRT forces the SONIC-16 to finish the current DMA operation as above however

the SONIC-16 will not retry until BRT is deasserted and the BR bit in the ISR (see Section 436) has been reset

Hence the mode has been latched on until the BR bit is cleared

Note

Unless LBR is set to a ‘‘1’’ BRT must remain asserted at least until the SONIC-16 has gone idle See Section 546 and the timing for Bus

Retry in Section 70

12 11

PO1 PO0 PROGRAMMABLE OUTPUTS

The PO1PO0 bits individually control the USR10 pins respectively when SONIC-16 is a bus master (HLDA or

BGACK is active) When PO1PO0 are set to a 1 the USR1USR0 pins are high during bus master operations and

when these bits are set to a 0 the USR1USR0 pins are low during bus master operations

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