The MAX3221 has just one driver and one receiver. For applications that use all
eight of the signals in a 9-wire interface, chips are available with three drivers
and five receivers (for DTEs) and with five drivers and three receivers (for
DCEs).
Some chips have faster, non-RS-232-compliant slew rates to allow operation at
up to 1 Mbps. To support a faster bit rate in both directions, the interfaces at
both ends must use faster components. An example of a chip that supports
faster bit rates is the MAX3225.
,- .
Many chips include power-saving features. A Shutdown input can place the
chip in a reduced-power mode. Some chips have a separate Enable input that
enables the receiver on detecting incoming data even if in shutdown mode.
Inside RS-232
51
Figure 4-1: Chips like the MAX232 and MAX233A simplify interfacing 5V logic to
RS-232.
Chapter 4
52
The MAX3212 has several advanced power-saving features. When all of the
RS-232 inputs are less than +3V and greater than -3V, the chip assumes the
inputs are open (not connected) and switches to low-power mode. On detecting
an input equal to or more positive than +2.7V or equal to or more negative
than -2.7V, the chip exits the low-power mode and begins normal operation.
Additional inputs enable software to place the chip in and out of low-power
mode. The chip??™s Receiver Enable Control input can save power by placing the
outputs of all receivers in a high-impedance state.
Pages:
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82