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author | 2018-01-28 13:19:53 -0500 | |
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committer | 2018-01-28 13:20:15 -0500 | |
commit | 515fc54f57d2b33da1929cb14b54fc89db41b7aa (patch) | |
tree | 0da90371a503e6781ce41ff775dd1b310655eda1 | |
parent | 33de68c7208f6addfc995d2551cea8d82457b608 (diff) |
74157.cpp: Update notes (nw)
-rw-r--r-- | src/devices/machine/74157.cpp | 12 |
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" |