á
PRELIMINARY
DS3 UNI FOR ATM
XRT7245
REV. 1.03
43
3.2.2.1.1.2
Whenever an Intel-type μC/μP wishes to write a byte
or word of data into a register or buffer location, with-
in the UNI, it should do the following.
Assert the ALE_AS (Address Latch Enable) input
pin by toggling it “high”. When the μC/μP asserts
the ALE_AS input pin, it enables the “Address
Bus Input Drivers” within the UNI chip.
Place the address of the “target” register or
buffer location (within the UNI), on the Address
Bus input pins, A[8:0].
While the μC/μP is placing this address value
onto the Address Bus, the Address Decoding cir-
cuitry (within the user’s system) should assert
the CS* input pin of the UNI device by toggling it
“l(fā)ow”. This step enables further communication
between the μC/μP and the UNI Microprocessor
Interface block.
After allowing the data on the Address Bus pins
to settle (by waiting the appropriate “Address
Setup” time); the μC/μP should toggle the
ALE_AS input pin “l(fā)ow”. This step causes the
UNI device to “l(fā)atch” the contents of the “Address
Bus” into its internal circuitry. At this point, the
The Intel Mode Write Cycle
1.
2.
3.
4.
address of the register or buffer location (within
the UNI), has now been selected.
Next, the μC/μP should indicate that this current
bus cycle is a “Write” Operation; by toggling the
WRB_RW (Write Strobe) input pin “l(fā)ow”. This
action also enables the “bi-directional” data bus
input drivers of the UNI device.
The μC/μP should then place the byte or word
that it intends to write into the “target” register, on
the bi-directional data bus, D[15:0].
After waiting the appropriate amount of time, for
the data (on the bi-directional data bus) to settle;
the μC/μP should toggle the WRB_RW (Write
Strobe) input pin “high”. This action accom-
plishes two things:
It latches the contents of the bi-directional
data bus into the XRT7245 DS3 UNI Micro-
processor Interface block.
It terminates the write cycle.
5.
6.
7.
a.
b.
Figure 9 presents a timing diagram which illustrates
the behavior of the Microprocessor Interface signals,
during an “Intel-type” Programmed I/O Write Operation.
F
IGURE
8. B
EHAVIOR
OF
M
ICROPROCESSOR
I
NTERFACE
SIGNALS
DURING
AN
“I
NTEL
-
TYPE
” P
ROGRAMMED
I/O R
EAD
O
PERATION
.
ALE_AS
RDB_DS
A[8:0]
CS*
D[15:0]
Rdy_Dtck
Not Valid
Valid
Address of Target Register
WRB_RW