Texas Instruments 990 Operation Manual page 13

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Central Processing Unit. The 990/4 CPU has the following characteristics:
• Eight interrupts (up to seven external and a power-up trap)
• Real-time clock
• Communications Register Unit (CRU) interface for I/O
• Direct Memory Access (DMA) interface for extended memory, which can be used for
processor-independent I/O (when a user-designed controller is implemented)
• Self-test routine
• Fault indicator
Memory. The minimum memory required for the Prototyping System Software is 4096 words of
on-board dynamic RAM, 512 words of on-board ROM for the 733 ASR loader and the self-test
feature, and 4096 words of dynamic RAM on a memory expansion circuit card. The expansion
card may be expanded to 20K words, giving a total of 24K words of dynamic RAM in the
Prototyping System configuration. The 512 words of ROM are divided into 256 words of
firmware for the 733 ASR ROM loader (both tape cassette and cards) and programmer panel and
256 words for the CPU/memory self-test routines. The card loader is included for compatibility
with the 990/1 0 Computer. ROM or static RAM may be expanded by an additional 512 words.
An additional EPROM memory expansion card is available. This card may contain from 1 K to
8K memory words in 1 K increments.
o
,
EOOO
F800
FAOO
FCOO
FEOO
FFFE
(A)133370
DYNAMIC RAM
(990/4 CONTAINS 4K WORDS
ON CPU BOA'RD.)
UNAVAILABLE AREA
ADDRESS LOCATIONS
28K TO 31 K
256 WORDS OF RAM OR ROM
EXPANSION
256 WORDS OF RAM OR ROM
EXPANSION
256 WORDS OF ROM
256 WORDS OF ROM
Figure 1-2, Hardware Memory Configuration
1-3
f
,
Digital Systems Division