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.

9

10

General-Purpose Active-Low Input. Read via the CTS register bit; often used for RS-232 clear-

to-send input (Table 1).

10

11

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.

11

13

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).

12

14

Asynchronous Serial-Data (transmitter) Output

13

15

Active-Low Interrupt Output. Open-drain interrupt output to microprocessor.

5

6

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.

6

7

Ground

7

8

Crystal Connection. Leave X2 unconnected for external clock. See

Crystal-Oscillator

Operation—X1, X2 Connection section.

8

9

Active-Low Chip-Select Input. DOUT goes high impedance when CS is high. IRQ, TX, and RTS

are always active. Schmitt-trigger input.

4

4

SPI/Microwire Serial-Clock Input. Schmitt-trigger input.

3

3

SPI/Microwire Serial-Data Output. High impedance when CS is high.

2

2

SPI/Microwire Serial-Data Input. Schmitt-trigger input.

1

1

X1

CTS

RTS

RX

TX

IRQ

SHDN

GND

X2

CS

SCLK

DOUT

DIN

Positive Supply Pin (2.7V to 5.5V)

14

16

No Connection. Not internally connected.

—

5, 12

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).