Texas Instruments 99/4A - Page 85

CLOCK
The TMS 9919 uses a 3.5S MHz clock signal on sin 14.. derived from
j- K a T M Q QQ 1 P \ / i H a q H 1 ~ p 1 S V p r OC “ i - OTH a ‘ A1\I(Aa A O A   d d — y H d U U V A
KHz GROM clock.
1. External sound from the cassette interface connector.
2. Sound from the speech unit.
R501 is used to reduce the speech signal to an appropriate level.
SOUND OUTPUT
Sound is available on pin 7. C502 and R511 are used to reduce the
bandwidth.. C503, 0504 and L501 are used for the same purpose.
DATA BUS
The TMS 9919 uses an eight bit parallel data bus connected
h i recti y to the 9 9 / 4 d a. t a h u s
SOUND PROCESSOR SELECTION LOGIC
The logic which selects the sound processor is given in -Figure 3C l
READY
The READY line of the TMS 9919 is directly connected to the system
READY line. This wired-OR convention is possible because HAND
gate U50G is an open collector.
WE
The WE signal distinguishes between a write to or a read from the
TMS 9919. ’
EXTERNAL SOUND
External sound is -Fed to pin 9 of the TMS 9919. The 99/4 svstem
uses two sound signals on pin 9.