CS 2734
Computer Organization II
Lecture 38: Buses
- 4/21/97
Read pages 111-120 (Sections 3.4.1 - 3.4.4) of Tanenbaum
- Floating point conversions
By popular request, we'll go over the following floating point
conversions:
- has a representation 3F000000H.
- has a representation 3F800000H.
- has a representation 3FC00000H.
- Categories of control lines:
- Bus control
- Interrupts
- Bus arbitration
- Coprocessor signaling
- Status
- Other
- Some terminology:
- Pinout refers to the meaning of signals on various pins
of a chip (address, data, control).
- Asserted means to cause an action. (For example A is
asserted high, but NOT A is asserted low.)
- Negated is the opposite of asserted.
- A bus is an electrical pathway between multiple devices.
- The rules for accessing the bus are called the bus protocol.
- A bus master is an active device that can initiate
a bus transfer.
- A slave is a passive device that can only wait for
requests.
- Synchronous bus:
- Driven by a crystal.
- Cycles of fixed length.
- The original PC bus and its extensions are examples
of synchronous bus technology.
Control on a synchronous bus is a little simpler, but the fixed cycle
limits the use of new faster technology.
- Asynchronous bus:
- Control done by master slave handshake with
MSYN
and SSYN line.
- More flexible.
- The VME bus is an example of asynchronous bus technology.
SKILL: You should understand how a bus works.
Revision Date: 4/21/97 at 7 p.m.