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MAX3100ETG-T

SPI/Microwire-Compatible UART in QSOP-16

Maxim Integrated 

MAX3100

SPI/MICROWIRE-Compatible

UART in QSOP-16

Table 5. Bit Descriptions (continued)

BIT

NAME

READ/

WRITE

RA/FE

r

SHDNi

w

SHDNo

r

ST

w

ST

r

T

r

TE

w

TM

w

TM

r

POR

STATE

0

0

0

0

0

1

0

0

0

DESCRIPTION

Receiver-Activity/Framing-Error Bit. In shutdown mode, this is the RA bit. In normal operation,

this is the FE bit. In shutdown mode, a transition on RX sets RA = 1. In normal mode, a fram-

ing error sets FE = 1. A framing error occurs if a zero is received when the first stop bit is

expected. FE is set when a framing error occurs, and cleared upon receipt of the next proper-

ly framed character independent of the FIFO being enabled. When the device wakes up, it is

likely that a framing error will occur. This error can be cleared with a write configuration. The

FE bit is not cleared on a Read Data operation. When an FE is encountered, the UART resets

itself to the state where it is looking for a start bit.

Software-Shutdown Bit. Enter software shutdown with a write configuration where SHDNi = 1.

Software shutdown takes effect after CS goes high, and causes the oscillator to stop as soon

as the transmitter becomes idle. Software shutdown also clears R, T, RA/FE, D0r–D7r,

D0t–D7t, Pr, Pt, and all data in the receive FIFO. RTS and CTS can be read and updated

while in shutdown. Exit software shutdown with a write configuration where SHDNi = 0. The

oscillator restarts typically within 50ms of CS going high. RTS and CTS are unaffected. Refer

to the Pin Description for hardware shutdown (SHDN input).

Shutdown Read-Back Bit. The read-configuration register outputs SHDNo = 1 when the UART

is in shutdown. Note that this bit is not sent until the current byte in the transmitter is sent (T =

1). This tells the processor when it may shut down the RS-232 driver. This bit is also set imme-

diately when the device is shut down through the SHDN pin.

Transmit-Stop Bit. One stop bit will be transmitted when ST = 0. Two stop bits will be transmit-

ted when ST = 1. The receiver only requires one stop bit.

Reads the value of the ST bit.

Transmit-Buffer-Empty Flag. T = 1 means that the transmit buffer is empty and ready to

accept another data word.

Transmit-Enable Bit. If TE = 1, then only the RTS pin will be updated on CS’s rising edge. The

contents of RTS, Pt, and D0t–D7t transmit on CS’s rising edge when TE = 0.

Mask for T bit. IRQ is asserted if TM = 1 and T = 1 (Table 6).

Reads the value of the TM bit (Table 6).

PE = 0, L = 0

IDLE

START D0 D1 D2 D3 D4 D5 D6 D7 STOP STOP IDLE

PE = 0, L = 1

IDLE

START D0 D1 D2 D3 D4 D5 D6 STOP STOP IDLE

PE = 1, L = 0

IDLE

START D0 D1 D2 D3 D4 D5 D6 D7 Pt STOP STOP IDLE

PE = 1, L = 1

IDLE

START D0 D1 D2 D3 D4 D5 D6 Pt STOP STOP IDLE

TIME

SECOND STOP BIT IS OMITTED IF ST = 0.

Figure 5. Parity and Word-Length Control

10

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