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author AJR <ajrhacker@users.noreply.github.com>2018-01-28 13:19:53 -0500
committer AJR <ajrhacker@users.noreply.github.com>2018-01-28 13:20:15 -0500
commit515fc54f57d2b33da1929cb14b54fc89db41b7aa (patch)
tree0da90371a503e6781ce41ff775dd1b310655eda1
parent33de68c7208f6addfc995d2551cea8d82457b608 (diff)
74157.cpp: Update notes (nw)
-rw-r--r--src/devices/machine/74157.cpp12
1 files changed, 10 insertions, 2 deletions
diff --git a/src/devices/machine/74157.cpp b/src/devices/machine/74157.cpp
index 6321e9c88dd..8ca2cae3617 100644
--- a/src/devices/machine/74157.cpp
+++ b/src/devices/machine/74157.cpp
@@ -5,11 +5,19 @@
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
- other purposes.
+ Often used to help feed 8-bit ROM data into a MSM5205 (which may
+ require additional pullups for CMOS compatibility), and for many other
+ purposes.
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"