XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
40
3.2
Interfacing the XRT7245 DS3 UNI to the
Local μC/μP Over Via the Microprocessor
Interface Block
The Microprocessor Interface block, within the UNI
device is very flexible and provides the following
options to the user.
To interface the UNI device to a μC/μP over an 8-bit
or 16-bit wide bi-directional data bus.
To interface the UNI to an Intel-type or Motorola-
type μC/μP
To transfer data (between the UNI IC and the μC/μP)
via the Programmed I/O or Burst Mode
Each of the options are discussed in detail below.
Section 3.2.1 will discussed the issues associated
with interfacing the UNI to a μC/μP over an 8-bit wide
and 16-bit wide bi-directional data bus. Afterwards,
Section 3.2.2 will discuss Data Access (e.g.,
Programmed I/O and Burst) Mode when interfaced to
both Motorola-type and Intel-type μC/μP
3.2.1
Interfacing the XRT7245 DS3 UNI to the
Microprocessor Over an 8 and 16 Bit
Wide Bi-Directional Data Bus
The XRT7245 DS3 UNI Microprocessor Interface
permits the user to interface it to a μC/μP over an 8 or
16-bit wide bi-directional data bus.
If the user wishes to interface the UNI to a μC/μP
over an 8-bit wide bi-directional data bus, then he/
she should tie the “Width16” input pin to GND. In this
mode, only data bus pins: D0 through D7 will be active.
The remaining eight data bus pins (e.g., D8 through
D15) will be inactive.
Conversely, if the user wishes to interface the UNI to
a μC/μP over a 16-bit bi-directional data bus, then he/
she should tie the “Width16” input pin to VDD. In this
mode, all of the data bus pins: D0 through D15 will be
active.
The next two sections present issues associated with
interfacing the DS3 UNI to the μC/μP over an 8-bit
wide and 16-bit wide bi-directional data bus, respec-
tively.
T
ABLE
3: P
IN
D
ESCRIPTION
OF
THE
M
ICROPROCESSOR
I
NTERFACE
S
IGNALS
WHILE
THE
M
ICROPROCESSOR
I
NTERFACE
IS
OPERATING
IN
THE
M
OTOROLA
M
ODE
P
IN
N
AME
E
QUIVALENT
P
IN
IN
M
OTOROLA
E
NVIRONMENT
T
YPE
D
ESCRIPTION
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 indicates a Read Cycle. When this
pin is “l(fā)ow”, 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.