USB97C201 datasheet(48/59 Pages) SMSC

48 / 59 page

SMSC USB97C201

Page 48

Rev. 11-05-03

DATASHEET

Termination Phase: Either the source or the receiver can terminate a burst transfer. A burst termination consists

of a Stop Request, Stop Acknowledge and transfer of CRC data.

The USB97C201 can stop a burst by asserting STOP, with the IDE device acknowledged by deasserting

DRQ.

The IDE device stops a burst by deasserting DRQ and the USB97C201 acknowledges by asserting STOP.

The source then drives the STROBE signal to a high level. The USB97C201 then drive the CRC value onto

the data lines and deassert nDACK. The IDE devices will latch the CRC value on the rising edge of nDACK.

The USB97C201 will terminate a burst transfer if a Programmed I/O (PIO) cycle is executed to the IDE channel

currently running the burst, or upon transferring the last data from the final PRD.

At the completion of the entire transfer process, the IDE device will issue an interrupt, setting the ATA_IRQ bit and

forcing the remaining data to be sent to host on read operations.

6.3.6.3

Cyclic Redundancy Checking (CRC) Calculation

Cyclic Redundancy Checking (CRC-16) is used for error checking on Ultra ATA/66 transfers. The CRC value is

calculated for all data by both the USB97C201 and the IDE device over the duration of the DMA burst transfer

segment. This segment is defined as all data transferred with a valid STROBE edge from DACK assertion to nDACK

deassertion. At the end of the transfer burst segment, the USB97C201 will drive the CRC value onto the D[15:0]

signals. The value is then latched by the IDE device on deassertion of nDACK. The IDE device compares the

USB97C201 CRC value to its own and reports an error if there is a mismatch.

6.4 SRAM Buffers

1.25K Bytes of Buffer SRAM are provided. The Memory Map of the buffers are given below:

Table 64 –Buffer SRAM Mapping

SRAM ADDRESS

BUFFER DESCRIPTION

0x300 – 0x4FF

SRAM B 512 byte EP2/ATA buffer

0x100 – 0x2FF

SRAM A 512 byte EP2/ATA buffer

0x0C0 – 0x0FF

64 Byte EP1 TX Buffer

0x080 – 0x0BF

64 Byte EP1 RX Buffer

0x040 – 0x07F

64 Byte EP0 TX Buffer

0x000 – 0x03F

64 Byte EP0 RX Buffer

Note: The above SRAM address in the table refers to the BYTE location within the SRAM. The SRAM is actually

physically organized as a 32 bit wide memory.

The buffers used for EP2 is organized as two 512 byte buffers: A and B. The A buffer has its address starting at

0X100, while the B is at address 0X300.. Byte counts for data received or to be transmitted is contained in the

RAMWRBC_A/B and RAMRDBC

_A/B register sets, respectively. The direction of data flow is determined by the DIR

bit in the EP2 Control register. If DIR=0 then data flow is from the SIE to SRAM and from the SRAM to the ATA

interface. If DIR=1 the data flow is in the opposite direction. Unlike EP0 and EP1, data for both directions can not be

simultaneously buffered in the SRAM for EP2. However, the dual buffers and automatic transfer operation (see

Section 6.9) allow for sustained 480Mbps transfers across the USB97C201.

6.5 8051 Options

The following 8051 core options are included:

256 SRAM in SFR space

Three timers

Single serial port

Extended external inputs (INT2-13)

External program memory and external data bus (XDATA) are pinned out as a common bus.

6.6 Address Multiplexing

Access to the SRAM for the three access points, ie SIE, ATA DMA, or 8051, is via a time division multiplexing

scheme (See Section 6.7). Each of the above blocks have access to read or write the SRAM during one of four sub-

periods (the fourth period being reserved for future expansion/idle) of a four phase 15 Mhz clock( ie 60 Mhz slice

clock). The values set in the EPx_BUFx , and IN_BUFx, or OUT_BUFx (depending on the direction set for EP2)

control the address counter for accesses by the EPs during their time-slice.

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