1125: correct POR reset section

To close #67.

Co-authored-by: sb10q <sb@m-labs.hk>
Reviewed-on: sinara-hw/datasheets#72
Co-authored-by: architeuthis <am@m-labs.hk>
Co-committed-by: architeuthis <am@m-labs.hk>

2118-2128.tex

@@ -34,9 +34,9 @@ The 2118 BNC-TTL card is an 8hp EEM module; the 2128 SMA-TTL is a 4hp EEM module
 
 Each card provides two banks of four digital channels, for a total of eight digital channels, with respectively either BNC (2118) or SMA (2128) connectors. Each bank possesses individual ground isolation. The direction (input or output) of each bank can be selected using DIP switches, and applies to all four channels of the bank.
 
-Each channel supports 50\textOmega~terminations, individually controllable using DIP switches. Outputs tolerate short circuits indefinitely.
+Each channel supports 50\textOmega~terminations, individually controllable using DIP switches. Outputs tolerate short circuits indefinitely. Both cards are capable of a minimum pulse width of 3ns.
 
-Both cards are capable of a minimum pulse width of 3ns.
+Note that isolated TTL cards are less suited to low-noise applications as the isolator itself injects noise between primary and secondary sides. Cable shields may also radiate EMI from the isolated grounds. For low-noise applications, use non-isolated cards such as 2238 MCX-TTL or 2245 LVDS-TTL.
 
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