Rainbow Electronics MAX3420E - Manual (Page 2)

The MAX3420E connects to any microprocessor using
3 or 4 interface pins (Figure 1). On a simple micro-
processor without SPI hardware, these can be bit-
banged general-purpose I/O pins. Four GPIN and four
GPOUT pins on the MAX3420E more than replace the
µP pins necessary to implement the interface. Although
the MAX3420E SPI hardware includes separate data-in
(MOSI, (Master-Out, Slave-In)) and data-out (MISO,
(Master-In, Slave-Out)) pins, the SPI interface can also
be configured for the MOSI pin to carry bidirectional
data, saving an interface pin. This is referred to as half-
duplex mode.
Two MAX3420E features make it easy to connect to
large, fast chips such as ASICs and DSPs (see Figure
2). First, the SPI interface can be clocked up to 26MHz.
Second, a V
L
pin and internal level translators allow
running the system interface at a lower voltage than the
3.3V required for V
CC .
The MAX3420E provides an ideal method for electrically
isolating a USB interface (Figure 3). USB employs flow
control in which the MAX3420E automatically answers
host requests with a NAK handshake, until the micro-
processor completes its data-transfer operations over
the SPI port. This means that the SPI interface can run
at any frequency up to 26MHz. Therefore, the designer
is free to choose the interface operating frequency and
to make opto-isolator choices optimized for cost or per-
formance.
MAX3420E
USB Peripheral Controller
with SPI Interface
2 _______________________________________________________________________________________
Typical Application Circuits
3.3V
REGULATOR
SPI
3, 4
INT
USB µP
MAX3420E
3.3V
REGULATOR
POWER RAIL
ASIC,
DSP,
ETC.
SPI
3, 4
INT MAX3420E
USB
Figure 2. The MAX3420E Connected to a Large Chip
3.3V
REGULATOR
MISO
LOCAL
GND
LOCAL
POWER
INT
MAX3420E
SCLK
MOSI
SS
MICRO
ASIC
DSP
I
S
O
L
A
T
O
R
S
USB
Figure 3. Optical Isolation of USB Using the MAX3420E
Figure 1. The MAX3420E connects to any microprocessor
using 3 or 4 interface pins.