AT83SND2CMP3B datasheet(131/241 Pages) ATMEL

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4341F–MP3–03/06

AT8xC51SND2C/MP3B

17. IDE/ATAPI Interface

The AT8xC51SND2C provides an IDE/ATAPI interface allowing connection of devices such as

CD-ROM reader, CompactFlash cards, Hard Disk Drive, etc. It consists of a 16-bit data transfer

(read or write) between the AT8xC51SND2C and the IDE device.

17.1

Description

The IDE interface mode is enabled by setting the EXT16 bit in AUXR (see Figure 7-5, page 29).

As soon as this bit is set, all MOVX instructions read or write are done in a 16-bit mode compare

to the standard 8-bit mode. P0 carries the low order multiplexed address and data bus (A7:0,

D7:0) while P2 carries the high order multiplexed address and data bus (A15:8, D15:8). When

writing data in IDE mode, the ACC contains D7:0 data (as in 8-bit mode) while DAT16H register

(see Table 17-2) contains D15:8 data. When reading data in IDE mode, D7:0 data is returned in

ACC while D15:8 data is returned in DAT16H.

Figure 17-1 shows the IDE read bus cycle while Figure 17-2 shows the IDE write bus cycle. For

simplicity, these figures depict the bus cycle waveforms in idealized form and do not provide pre-

cise timing information. For IDE bus cycle timing parameters refer to the Section “AC

Characteristics”.

IDE cycle takes 6 CPU clock periods which is equivalent to 12 oscillator clock periods in stan-

dard mode or 6 oscillator clock periods in X2 mode. For further information on X2 mode, refer to

the Section “X2 Feature”, page 14.

Slow IDE devices can be accessed by stretching the read and write cycles. This is done using

the M0 bit in AUXR. Setting this bit changes the width of the RD and WR signals from 3 to 15

CPU clock periods.

Figure 17-1.

IDE Read Waveforms

Notes:

1. RD signal may be stretched using M0 bit in AUXR register.

2. When executing MOVX @Ri instruction, P2 outputs SFR content.

3. When executing MOVX @DPTR instruction, if DPHDIS is set (Page Access Mode), P2 out-

puts SFR content instead of DPH.

ALE

RD(1)

DPL or Ri

D7:0

CPU Clock

DPH or P2

(2),(3)

D15:8

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