MAX3100
SPI/Microwire-Compatible
UART in QSOP-16
_______________________________________________________________________________________ 5
______________________________________________________________Pin Description
Crystal Connection. X1 also serves as an external clock input. See
Crystal-Oscillator
Operation—X1, X2 Connection
section.
910
General-Purpose Active-Low Input. Read via the CTS register bit; often used for RS-232 clear-
to-send input (Table 1).
1011
General-Purpose Active-Low Output. Controlled by the RTS register bit. Often used for
RS-232 request-to-send output or RS-485 driver enable.
1113
Asynchronous Serial-Data (receiver) Input. The serial information received from the modem or
RS-232/RS-485 receiver. A transition on RX while in shutdown generates an interrupt (Table 5).
1214
Asynchronous Serial-Data (transmitter) Output1315
Active-Low Interrupt Output. Open-drain interrupt output to microprocessor.56
Hardware-Shutdown Input. When shut down (SHDN = 0), the oscillator turns off immediately
without waiting for the current transmission to end, reducing supply current to just leakage
currents.
67
Ground78
Crystal Connection. Leave X2 unconnected for external clock. See
Crystal-Oscillator
Operation—X1, X2 Connection
section.
89
Active-Low Chip-Select Input. DOUT goes high impedance when CS is high. IRQ, TX, and RTS
are always active. Schmitt-trigger input.
44
SPI/Microwire Serial-Clock Input. Schmitt-trigger input.33
SPI/Microwire Serial-Data Output. High impedance when CS is high.
22
SPI/Microwire Serial-Data Input. Schmitt-trigger input.11
X1
CTS
RTS
RX
TX
IRQ
SHDN
GND
X2
CS
SCLK
DOUT
DIN
Positive Supply Pin (2.7V to 5.5V)1416
No Connection. Not internally connected.—5, 12
V
CC
N.C.
PIN
QSOP
FUNCTION
DIP
NAME
_______________Detailed Description
The MAX3100 universal asynchronous receiver trans-
mitter (UART) interfaces the SPI/Microwire-compatible,
synchronous serial data from a microprocessor (µP) to
asynchronous, serial-data communication ports (RS-
232, RS-485, IrDA). Figure 2 shows the MAX3100 func-
tional diagram.
The MAX3100 combines a simple UART and a baud-rate
generator with an SPI interface and an interrupt genera-
tor. Configure the UART by writing a 16-bit word to a
write-configuration register, which contains the baud rate,
data-word length, parity enable, and enable of the 8-word
receive first-in/first-out (FIFO). The write configuration
selects between normal UART timing and IrDA timing,
controls shutdown, and contains 4 interrupt mask bits.
Transmit data by writing a 16-bit word to a write-data
register, where the last 7 or 8 bits are actual data to be
transmitted. Also included is the state of the transmitted
parity bit (if enabled). This register controls the state of
the RTS output pin. Received words generate an inter-
rupt if the receive-bit interrupt is enabled.
Read data from a 16-bit register that holds the oldest
data from the receive FIFO, the received parity data,
and the logic level at the CTS input pin. This register
also contains a bit that is the framing error in normal
operation and a receive-activity indicator in shutdown.
The baud-rate generator determines the rate at which the
transmitter and receiver operate. Bits B0 to B3 in the
write-configuration register determine the baud-rate divi-
sor (BRD), which divides down the X1 oscillator frequen-
cy. The baud clock is 16 times the data rate (baud rate).
The transmitter section accepts SPI/Microwire data, for-
mats it, and transmits it in asynchronous serial format
from the TX output. Data is loaded into the transmit-
buffer register from the SPI/Microwire interface. The
MAX3100 adds start and stop bits to the data and
clocks the data out at the selected baud rate (Table 7).
