á
PRELIMINARY
DS3 UNI FOR ATM
XRT7245
REV. 1.03
45
3.2.2.1.2.2
Whenever a Motorola-type μC/μP wishes to write a
byte or word of data into a register or buffer location,
within the UNI, it should do the following.
Assert the ALE_AS (Address Select) input pin by
toggling it “l(fā)ow”. This step 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* (Chip Select) input pins of the UNI by
toggling it “l(fā)ow”. This step enables further com-
munication 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 “high”. This step causes the
UNI device to “l(fā)atch” the contents of the “Address
Bus” into its own circuitry. At this point, the
Address of the register or buffer location (within
the UNI), has now been selected.
Further, the μC/μP should indicate that this cur-
rent bus cycle is a “Write” operation by toggling
the WRB_RW (R/W*) input pin “l(fā)ow”.
The Motorola Mode Write Cycle
1.
2.
3.
4.
5.
6.
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].
Next, the μC/μP should initiate the bus cycle by
toggling the RdB_DS (Data Strobe) input pin
“l(fā)ow”. When the XRT7245 DS3 UNI device
senses that the WRB_RW (R/W*) input pin is
“high” and that the RdB_DS (Data Strobe) input
pin has toggled “l(fā)ow”, it will enable the “input
drivers” of the bidrectional data bus, D[15:0].
After waiting the appropriate time, for this newly
placed data to settle on the bi-directional data
bus (e.g., the “Data Setup” time) the UNI will
assert the Rdy_Dtck output signal.
After the μC/μP detects the Rdy_Dtck signal
(from the UNI), the μC/μP should toggle the
RdB_DS input pin “high”. This action accom-
plishes two things.
It latches the contents of the bi-directional
data bus into the XRT7245 DS3 Micropro-
cessor Interface block.
It terminates the “Write” cycle.
7.
8.
9.
a.
b.
Figure 11 presents a timing diagram which illustrates
the behavior of the Microprocessor Interface signals,
during a “Motorola-type” Programmed I/O Write
Operation.
F
IGURE
10. I
LLUSTRATION
OF
THE
B
EHAVIOR
OF
M
ICROPROCESSOR
I
NTERFACE
SIGNALS
,
DURING
A
“M
OTOROLA
-
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 Data
Address of Target Register
WRB_RW