____________________Function Tables

Devices with Receiver/Driver Enable

(MAX3483/MAX3485/MAX3486/MAX3491)

Table 1. Transmitting

* B and A outputs are Z and Y, respectively, for full-duplex part

(MAX3491).

X = Don’t care; High-Z = High impedance

Table 2. Receiving

* DE is a “don’t care” (x) for the full-duplex part (MAX3491).

X = Don’t care; High-Z = High impedance

Devices without Receiver/Driver Enable

(MAX3488/MAX3490)

Table 3. Transmitting

Table 4. Receiving

__________Applications Information

The MAX3483/MAX3485/MAX3486/MAX3488/MAX3490/

MAX3491 are low-power transceivers for RS-485 and

RS-422 communications. The MAX3483 and MAX3488

can transmit and receive at data rates up to 250kbps,

the MAX3486 at up to 2.5Mbps, and the MAX3485/

MAX3490/MAX3491 at up to 10Mbps. The MAX3488/

MAX3490/MAX3491 are full-duplex transceivers, while

the MAX3483/MAX3485/MAX3486 are half-duplex.

Driver Enable (DE) and Receiver Enable (RE) pins are

included on the MAX3483/MAX3485/MAX3486/

MAX3491. When disabled, the driver and receiver out-

puts are high impedance.

Reduced EMI and Reflections

(MAX3483/MAX3486/MAX3488)

The MAX3483/MAX3488 are slew-rate limited, minimiz-

ing EMI and reducing reflections caused by improperly

terminated cables. Figure 13 shows both the driver

output waveform of a MAX3485/MAX3490/MAX3491

transmitting a 125kHz signal and the Fourier analysis of

that waveform. High-frequency harmonics with large

amplitudes are evident. Figure 14 shows the same infor-

mation, but for the slew-rate-limited MAX3483/MAX3488

transmitting the same signal. The high-frequency har-

monics have much lower amplitudes, and the potential for

EMI is significantly reduced.

Low-Power Shutdown Mode

(MAX3483/MAX3485/MAX3486/MAX3491)

A low-power shutdown mode is initiated by bringing both

RE high and DE low. The devices will not shut down

unless both the driver and receiver are disabled (high

impedance). In shutdown, the devices typically draw

only 2nA of supply current.

assume the part was in the low-power shutdown mode;

driver was disabled, but the part was not shut down.

3.3V-Powered, 10Mbps and Slew-Rate-Limited

True RS-485/RS-422 Transceivers

______________________________________________________________________________________

11

INPUTS

OUTPUTS

RE

DE

DI

B*

A*

MODE

X

1

1

0

1

Normal

X

1

0

1

0

Normal

0

0

X

High-Z

High-Z

Normal

1

0

X

High-Z

High-Z

Shutdown

INPUTS

RE

DE

A, B

RO

MODE

0

0*

≥ +0.2V

1

Normal

0

0*

≤ -0.2V

0

Normal

0

0*

Inputs Open

1

Normal

1

0

X

High-Z

Shutdown

OUTPUTS

INPUTS

OUTPUT

A, B

RO

≥ +0.2V

1

≤ -0.2V

0

Inputs Open

1

INPUT

OUTPUTS

DI

Z

Y

1

0

1

0

1

0

5MHz

500kHz/div

0Hz

10dB/div

5MHz

500kHz/div

0Hz

10dB/div

Figure 13. Driver Output Waveform and FFT Plot of MAX3485/

MAX3490/MAX3491 Transmitting a 125kHz Signal

Figure 14. Driver Output Waveform and FFT Plot of MAX3483/

MAX3488 Transmitting a 125kHz Signal