Rainbow Electronics AT89C51SND1C - Manual (Page 133)

133
AT8xC51SND1C
4109E–8051–06/03
Table 121. External Data Memory Interface Signals
Registers Table 122. DAT16H Register
DAT16H (S:F9h) – Data 16 High Order Byte
Reset Value =XXXX XXXXb
Signal
Name Type Description
Alternate
Function
A15:8 I/O
Address Lines
Upper address lines for the external bus.
Multiplexed higher address and data lines for the IDE interface.
P2.7:0
AD7:0 I/O
Address/Data Lines
Multiplexed lower address and data lines for the IDE interface.
P0.7:0
ALE O
Address Latch Enable
ALE signals indicates that valid address information is available on lines
AD7:0.
-
RD O
Read
Read signal output to external data memory.
P3.7
WR O
Write
Write signal output to external memory.
P3.6
7 6 5 4 3 2 1 0
D15 D14 D13 D12 D11 D10 D9 D8
Bit
Number
Bit
Mnemonic Description
7 - 0 D15:8
Data 16 High Order Byte
When EXT16 bit is set, DAT16H is set by software with the high order data Byte
prior any MOVX write instruction.
When EXT16 bit is set, DAT16H contains the high order data Byte after any
MOVX read instruction.