_____________________Function Tables

Devices with Receiver/Driver Enable

(MAX3483E/MAX3485E/MAX3486E/MAX3491E)

Table 1. Transmitting

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

(MAX3491E).

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

Table 2. Receiving

* DE is a “don’t care” (x) for the full-duplex part (MAX3491E).

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

Devices without Receiver/Driver Enable

(MAX3488E/MAX3490E)

Table 3. Transmitting

Table 4. Receiving

___________Applications Information

The MAX3483E/MAX3485E/MAX3486E/MAX3488E/

MAX3490E/MAX3491E are low-power transceivers for

RS-485 and RS-422 communications. The MAX3483E

and MAX3488E can transmit and receive at data rates

up to 250kbps, the MAX3486E at up to 2.5Mbps, and the

MAX3485E/MAX3490E/MAX3491E at up to 12Mbps. The

MAX3488E/MAX3490E/MAX3491E are full-duplex trans-

ceivers, while the MAX3483E/MAX3485E/MAX3486E are

half-duplex. Driver Enable (DE) and Receiver Enable

(RE) pins are included on the MAX3483E/MAX3485E/

MAX3486E/MAX3491E. When disabled, the driver and

receiver outputs are high impedance.

Reduced EMI and Reflections

(MAX3483E/MAX3486E/MAX3488E)

The MAX3483E/MAX3488E are slew-rate limited, mini-

mizing EMI and reducing reflections caused by improp-

erly terminated cables. Figure 13 shows the driver

output waveform of a MAX3485E/MAX3490E/MAX3491E

transmitting a 125kHz signal, as well as the Fourier

analysis of that waveform. High-frequency harmonics

with large amplitudes are evident. Figure 14 shows the

same information, but for the slew-rate-limited

MAX3483E/MAX3488E transmitting the same signal. The

high-frequency harmonics have much lower amplitudes,

and the potential for EMI is significantly reduced.

Low-Power Shutdown Mode

(MAX3483E/MAX3485E/MAX3486E/MAX3491E)

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, ±15kV ESD-Protected, 12Mbps 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

0

10dB/div

5MHz

500kHz/div

0

10dB/div

Figure 13. Driver Output Waveform and FFT Plot of MAX3485E/

MAX3490E/MAX3491E Transmitting a 125kHz Signal

Figure 14. Driver Output Waveform and FFT Plot of

MAX3483E/ MAX3488E Transmitting a 125kHz Signal