MAX14890E Datasheet, PDF (24/30 Pages) Maxim Integrated Products – Overvoltage and Undervoltage Fault Detection

MAX14890E
Incremental Encoder Interface for RS-422,
HTL, and TTL with Digital Inputs
Table 11. SPI Mode RxA, RxB Selection Bits
_SNGL
0
0
1
1
_TTL
0
1
0
1
RxA, RxB RECEIVER
OPERATION
D-HTL
RS-422
SE-HTL
TTL
Table 12. SPI Mode RxZ Selection Bits
ZTTL ZSNGL
ZDI
0
0
0
0
1
0
1
0
0
1
1
0
X
X
1
X = Don’t care
RxZ RECEIVER
OPERATION
D-HTL
SE-HTL
RS-422
TTL
DI
Table 13. SPI Mode RxY Selection Bits
YTTL
0
YSNGL
0
RxY RECEIVER OPERATION
RS-422
0
1
DI
1
0
RS-422
1
1
TTL
Table 14. SPI Mode RxD2, RxD3 Selection
Bits
D_DI
0
1
RxD2, RxD3 RECEIVER
OPERATION
TTL
DI
Fault Diagnostics
In SPI mode, the interrupt output (D3FAULT/IRQ) and
associated _FAULT output asserts when a fault is detect-
ed on any receiver. _FAULT deasserts when the fault is
removed, but D3FAULT/IRQ remains latched until the
fault status is read through the SPI interface.
If the fault is not cleared, D3FAULT/IRQ deasserts after
the SPI read command, but the associated fault bit and
_FAULT output remain asserted.
Applications Information
Cable Termination
Transmission line termination is required for RS-422,
HTL, and TTL high-speed signals on long cables. For
RS-422 and TTL signal levels, 120Ω termination is com-
monly used to match the characteristic impedance of the
cable. For HTL signals, 270Ω/100pF AC-termination with
a series RC can be applied to reduce power dissipation.
Figure 12 shows a sample circuit of a termination scheme
to suit all of these operating modes. The 270Ω termination
can be permanently left in for all operating modes. For
high-speed RS-422 and TTL signals, the cable should
be terminated by its characteristic impedance to reduce
reflections. This can be done by switching in the parallel
resistor in these modes using a beyond-the-rails switch
like the MAX14777.
IN
216Ω
RECEIVER
OUT
270Ω
MAX14777
IN
Figure 12. Sample Termination Scheme for HTL, RS-422, and
TTL modes
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