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.
Description
The IDE interface mode is enabled by setting the EXT16 bit in AUXR (see Figure 30,
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 137) 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 78 shows the IDE read bus cycle while Figure 79 shows the IDE write bus cycle.
For simplicity, these figures depict the bus cycle waveforms in idealized form and do not
provide precise 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
standard mode or 6 oscillator clock periods in X2 mode. For further information on X2
mode, refer to the Section “X2 Feature”, page 12.
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 78. IDE Read Waveforms
CPU Clock
ALE
RD(1)
DPL or Ri
D7:0
P0
P2
P2
DPH or P2(2),(3)
D15:8
P2
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 outputs SFR content instead of DPH.
132
AT8xC51SND2C
4341D–MP3–04/05
ATMEL [ ATMEL ]
