
XRT7234
E3 UNI FOR ATM
x r
PRELIMINARY
REV. P1.0.0
40
Table 2.
Pin Description of Microprocessor Interface Signals—While the Microprocessor Interface is Operating in the Intel Mode.
Pin Name
Equivalent
Pin in Intel
Environment
Type
Description
ALE_AS
ALE
I
Address-Latch Enable: This “active-high” signal is used to latch the contents on the
address bus, A[8:0]. The contents of the Address Bus are latched into the A[8:0]
inputs on the falling edge of ALE_AS. Additionally, this signal can be used to indicate
the start of a burst cycle.
RdB_DS
RD*
I
Read Signal: This “active-low” input functions as the read signal from the local
μ
P.
When this signal goes “l(fā)ow”, the UNI Microprocessor Interface will place the con-
tents of the addressed register on the Data Bus pins (D[15:0]). The Data Bus pins
will be “tri-stated” once this input signal returns “high”.
WRB_RW
WR*
I
Write Signal: This “active-low” input functions as the write signal from the local
μ
P.
The contents of the Data Bus (D[15:0]) will be written into the addressed register (via
A[8:0]), on the rising edge of this signal.
Rdy_Dtck
READY*
O
Ready Output: This “active-low” signal is provided by the UNI device, and indicates
that the current read or write cycle is to be extended until this signal is asserted. The
local
μ
P will typically insert “WAIT” states until this signal is asserted. This output will
toggle “l(fā)ow” when the device is ready for the next Read or Write cycle.
Table 3. Pin Description of the Microprocessor Interface Signals while the Microprocessor Interface is operating in the Motorola Mode
Pin Name
Equivalent
Pin in
Motorola
Environment
Type
Description
ALE_AS
AS*
I
Address Strobe: This “active-low” signal is used to latch the contents on the address
bus input pins: A[8:0] into the Microprocessor Interface circuitry. The contents of the
Address Bus are latched into the UNI device on the rising edge of the ALE_AS signal.
This signal can also be used to indicate the start of a burst cycle.
RdB_DS
DS*
I
Data Strobe: This signal latches the contents of the bi-directional data bus pins into
the Addressed Register (within the UNI) during a Write Cycle.
WRB_RW
R/W*
I
Read/Write* Input: When this pin is “high”, it indicate a Read Cycle. When this pin is low,
it indicates a Write cycle.
Rdy_Dtck
DTACK*
O
Data Transfer Acknowledge: The UNI device asserts DTACK* in order to inform the
CPU that the present READ or WRITE cycle is nearly complete. The 68000 family of
CPUs requires this signal from its peripheral devices, in order to quickly and properly
complete a READ or WRITE cycle.