____________________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.
For these devices, the t
PSH
and t
PSL
enable times
assume the part was in the low-power shutdown mode;
the t
PZH
and t
PZL
enable times assume the receiver or
driver was disabled, but the part was not shut down.
3.3V-Powered, 10Mbps and Slew-Rate-Limited
True RS-485/RS-422 Transceivers
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
5MHz500kHz/div0Hz
10dB/div
5MHz500kHz/div0Hz
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
MAX3483/MAX3485/MAX3486/
MAX3488/MAX3490/MAX3491
