MAX155EVKIT-DIP Maxim Integrated, MAX155EVKIT-DIP Datasheet - Page 3

• Manufacturer Part Number: MAX155EVKIT-DIP
• Description: Data Conversion IC Development Tools Evaluation Kit for the MAX155
• Manufacturer: Maxim Integrated
• Series: MAX155, MAX156r

the MAX660 must be increased to 150µF. Refer to the
MAX660 data sheet for more information.
A MAX696 is used to generate the reset pulse and for
the watchdog function. The microprocessor (µP) is held
in reset for 50ms after the voltage on the low-line input
(LLIN) exceeds its threshold. The values of R1 and R2
are selected so that a 4.25V supply voltage (±0.24V)
trips the LL
The watchdog monitoring function issues a reset pulse
if the watchdog input is not toggled within the specified
period of time. By leaving the MAX696 OSC IN and
OSC SEL pins disconnected, the MAX696 watchdog
period is set to 1s. If the watchdog-enable jumper is
installed (see the Jumper Options section for details),
the µP must toggle the watchdog input once a second
to prevent a reset pulse. Removing this jumper while
the system is running causes a reset.
For a complete description of the reset and watchdog
functions, refer to the MAX696 data sheet.
The MAX155 EV kit uses the 80C32 controller. The
80C32 is a member of the 8051 family that requires
external ROM for program storage. Internally, it has 256
bytes of RAM and four 8-bit input/output (I/O) ports.
Two of these ports (P0 and P2) are for operating the
address and data lines required by the external ROM,
RAM, and MAX155. A third (P3) is needed for the serial
link and I/O control lines. One of the pins of the remain-
ing port is for the watchdog circuit. The others are
available for the control of additional user circuits.
The on-board memory consists of 8kB of EPROM (the
27C64) holding the instructions for normal operations,
and 8kB of CMOS RAM (the 6264) to store conversion
results.
The user initiates a conversion at the keyboard of a per-
sonal computer running the MAX155 EV program. The
program sends an encoded conversion command over
the RS-232 link to the board. The 80C32 receives the
command, performs the MAX155 conversion, and
returns the results for display.
The 80C32 has a 16-bit address range (0000h to
FFFFh). The data bits on the 80C32 pins 32–39 multi-
plex the lower eight address bits. The 74CT573 latches
the address bits, and ROM and RAM use them as
A0–A7. The upper eight bits of the address field are not
multiplexed. Six of these bits, A8–A13, are sent directly
to the memory-address pins.
IN
comparator.
_______________________________________________________________________________________
Microprocessor Supervision
80C32 Microcontroller
Address Decoding
MAX155 Evaluation Kit
The two most significant bits of the address are decod-
ed and used to selectively enable ROM, RAM, or the
MAX155. The next two bits of the address field (A13
and A12) are also used in decoding the address range
for the MAX155. The MAX155 is accessed whenever a
location between C000h and CFFFh is addressed.
Table 1 shows the address range for each device.
The MAX155 on the EV kit is configured to use its internal
reference and to allow a bipolar input range. The MAX155
internal reference can be replaced by cutting the trace
across J6 and providing an external reference voltage.
The bipolar input range is facilitated by a -5V source con-
nected to V
open circuited to place the input range selection under
program control. See the Jumper Selection section for
details regarding the MODE selection pin.
The eight analog inputs are available at the board’s
edge. Each input has a 1kΩ resistor in series as protec-
tion against excessive short-circuit currents. The high-
input impedance allows this precaution without
introducing additional errors. There are two input
ranges for the MAX155. Either the unipolar (0 to 2.5V)
or bipolar (-2.5V to +2.5V) range can be selected under
program control. It is possible to hardwire the range
selection for other applications. In bipolar/differential
mode, the readings reflect the voltage between the two
analog inputs. For example, if the V
to +2.5V, input range is 0 to +5.0V. The output readings
(-2.50V to +2.49V) indicate the differential voltage
between V
operation with single supplies. See the MAX155 data
sheet for details.
Maxim took several precautions to reduce the system's
noise level. Users should consider noise reduction as
part of their design.
The data bus to the MAX155 is buffered by IC9, a
74HCT245 octal transceiver. This device isolates the
MAX155 from the digital signals constantly present on
the data bus. This reduces the noise level of any ana-
log-to-digital converter (ADC) in a digital environment.
Table 1. Address Range in Hexadecimal
A14, A15
00
01
10
11
11
SS
IN+
(pin 6). The MAX155 MODE selection pin is
ADDRESS RANGE
and V
C000
8000
D000
0000
4000
IN-
BFFF
. This allows bipolar/differential
3FFF
7FFF
CFFF
FFFF
IN-
DEVICE ENABLED
pin is referenced
Not used
Not used
MAX155
ROM
RAM
MAX155
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