Texas Instruments 99/4A - Page 18

GENERAL DESCRIPTION OF THE 99 /4A
The following paragraphs provide a description of the 99/4A system
hardware, the VDP chip (TMS 9913), the sound chip (TMS 9919), the
GROM (TMC 0430), the associated timing diagrams, the cassette
interface circuitry and power supply.
99/4 SYSTEM HARDWARE
The 99/4 has been built around the TMS 9900 microprocessor . Figure 1,
shows a block diagram of the system. In this description the logic of
the 99/4 is grouped into the fallowing functional sections.
< Clock generator/driver
• Microprocessor unit
• Memory selection logic
f System ROM & RAM
• 16 to 8 bit interfacing circuit
• Timing and control logic
• GROM memory
• TMS 9901 programmable system interface
• TMS 9918 video display processor
• TMS 9919 sound generator
• Keyboard, remote handheld unit
• Cassette interfacing circuit
• I/O port
• Power supply
• European power supply
* Audio board
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