AT&T 3B2/300 Technical Reference Manual page 284

- - - - - - - - - - - - - - - - - - - - - - - - - - - FUNCTIONAL DESCRIPTION.
SYSTEM BOARDS
The Version 2 382 computers have a CM190A/ED-4C637-30 System Board. The Version 3
computers have a CM518A/B/C System Board. The two styles of system boards are discussed in the
following sections.
CM190A/ED-4C637-30 System Board
Figure 3-13 is a functional block diagram of the Version 2 system board. The system board
functional description is based primarily on the System Board, ED-4C637-30. Collectively, the
382 computer system board features are listed below:
• Central Processing Unit (CPU)
• Memory Management Unit (MMU)
• Math Acceleration Unit (MAU) (not supported on CM190A, optional on ED-4C637-30)
• Address decoding for 15 input/output card chip selects
• Time-of-Day (TOD), periodic, sanity, and bus timers
• 16-bit Control and Status Register (CSR)
• Eight interrupt levels (three levels for feature cards)
• Two RS-232C serial ports with data set control
• Direct Memory Access Controller (DMAC) for integral hard disk, integral floppy disk, and
Universal Asynchronous Receiver/Transmitters (UARTs)
• 256 kilobytes to 4 megabytes of Dual Port Dynamic Random Access Memory (DPDRAM) with
hardware refresh and per-byte parity
• Supports 8- and 16-bit feature cards
• Power reset of system board and feature cards
• "Soft power" control
• IK by 4-bit Nonvolatile Random Access Memory (NVRAM)
• 3.6 volt DC lithium battery for NVRAM, TOD clock, and feature cards
• Supports dumb, programmed, and intelligent controller (feature) cards
• Supports feature card access of DPDRAM via daisy-chained Direct Memory Access (DMA)
arbitration
• Supports programmed to control feature card access
• No option straps required for feature card addresses or interrupt vectors.
Early versions of the system board differ in the physical configuration of the CPU and MMU;
however, except for the MAU capability and the system clock rate, the CMI 90A System Board is
functionally equivalent to the System Board, ED-4C637-30. Refer to Chapter 2, Equipment Description,
for information on the physical configuration of the CMI 90A System Board and System Board,
ED-4C637-30.
FUNCTIONAL DESCRIPTION 3-31