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74157.cpp: Update notes (nw)

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AJR 2018-01-28 13:19:53 -05:00
parent 33de68c720
commit 515fc54f57
1 changed files with 10 additions and 2 deletions
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src/devices/machine/74157.cpp
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@ -5,11 +5,19 @@
74LS157/74HCT157 Quad 2 to 1-Line Data Selectors/Multiplexers (TTL) 74LS157/74HCT157 Quad 2 to 1-Line Data Selectors/Multiplexers (TTL)
Often used to help feed 8-bit ROM data into a MSM5205, and for many Often used to help feed 8-bit ROM data into a MSM5205 (which may
other purposes. require additional pullups for CMOS compatibility), and for many other
purposes.
74LS158 has inverted outputs; 74LS157 is non-inverting. 74LS158 has inverted outputs; 74LS157 is non-inverting.
74LS257 and 74LS258 have three-state outputs with an active-low enable,
making these devices popular for bus-compatible applications which the
emulation here is not particularly suitable for. When pin 15 is tied to
GND, however, these devices become pin-compatible replacements for
74LS157 and 74LS158; this substitution is somewhat common on arcade
bootlegs.
***************************************************************************/ ***************************************************************************/
#include "emu.h" #include "emu.h"