Chapter 10

Input/Output Organization

Connections between a CPU and an I/O device

• Types of bus (Figure 10.1)– Address bus– Data bus– Control bus

Figure 10.1

10.1 Asynchronous data transfer

• Synchronous data transfer– It usually occur when peripherals are located within the

same computers as the CPU.– It shares a common clock.– Data does not have to travel very far physically.

• Asynchronous data transfer– It is used when synchronous transfers are not viable. – It uses control signals and their associated hardware to

coordinate the movement of data. – A common clock is not needed.

10.1 Asynchronous data transfer(continued)

• Types of asynchronous data transfer– Source-initiated data transfer– Destination-initiated data transfer– Handshaking– Destination-initiated data transfer with

handshaking

Source-initiated data transfer

• The source outputs its data, then strobes a control signal for a set amount of time.

• The destination device reads in the data during this time.

• Example: Figure 10.2

Figure 10.2

Destination-initiated data transfer

• The destination device initiates data transfer

• The destination device transmits a data strobe signal to the source device and after a set delay, the destination device reads in this data and desserts the data strobe.

• Example: Figure 10.3

Figure 10.3

Source-initiated data transfer with handshaking

• It is useful when the time of data transfer between the destination device and the source device.

• It uses an additional control signal, data acknowledge signal.

• Figure 10.4

Figure 10.4

Destination-initiated data transfer with handshaking

• It is useful when the time of data transfer between the destination device and the source device.

• It uses an additional control signal, data-ready signal.

• Figure 10.5

Figure 10.5

10.2 Programmed I/O

• Programmed I/O– A program instruction causes CPU to input or

output data.

• Input port– It makes data available to the CPU when the

CPU would read the data from the data bus.

10.2 Programmed I/O(continued)

• Thermostat control example– Read temperature(T) from external sensor.

– If (T thermostat setting+2) turn on air conditioner

– If (T thermostat setting and air conditioner is on) turn off air conditioner

– If (T thermostat setting-2) turn on heater

– If (T thermostat setting and air heater is on) turn off heater.

– Go to start of sequence

10.2 Programmed I/O(continued)

• Thermostat controller (program in Figure 10.7)– Memory mapped I/O

• 0FFFFH: input port (Figure 10.6)

• 0FFFEH: thermostat setting

• 0FFFDH: output port01 = turn on air conditioning 02 = turn off air conditioning

03 = turn on heat 04=turn off heat

• 1000H: current status00 = heat and air conditioning are both off

FF = heat on FE=air conditioning off

Figure 10.6

Figure 10.7

10.2 Programmed I/O(continued)

• Isolated I/O instructions (Table 10.1)– INPT

– OTPT

• Control Signal– IO/M’

10.2 Programmed I/O(continued)

• RTL of INPT instruction– INPT1: DR M, PC PC+1, ARAR+1

– INPT2: TRDR, DRM, PCPC+1

– INPT3: ARDR,TR

– INPT4: DRinput port

– INPT5: ACDR

• Figure 10.8– States to implement the INPT execute routine

• Figure 10.9 – Hardware to generate the state signals for the INPT execute

routine

Figure 10.8

Figure 10.9

10.3 Interrupts

• Interrupt– A mechanism for alleviating the delay for I/O.

• Polling (Refer to Figure 10.10)– The CPU sends a request to an I/O device.– The I/O device processes the request and sets a device-

ready signal when it is ready.– The CPU reads in this signal via another I/O address

and checks the value.– If the signal is set, it performs the data transfer. If not,

it loops back.

10.3 Interrupts(continued)

• Polling is relatively straightforward in design and programming. But a slow device causes the CPU to remain in the polling loop.– To make use of this wasteful CPU time,

interrupts were developed.• Interrupt request signal

• Interrupt acknowledge signal

10.3 Interrupts(continued)

• Types of interrupt– External interrupts– Internal interrupts– Software interrupts

10.3 Interrupts(continued)

• Processing interrupt: by interrupt handler– Do nothing until the current instruction has

been executed– Get the address of the handler routine(vector

interrupts)– Invoke the handler routine

Figure 10.10

10.3 Interrupts(continued)

Interrupt hardware and priority A non-vectored interrupt for a single device :Figure

10.11

A vectored interrupt for a single device :Figure 10.12

Figure 10.11

Figure 10.12

Multiple Devices

• Non-vectored interrupts : Figure 10.13

• Vectored interrupts– Daisy chaining (Figure 10.14)– Parallel priority(Figure 10.15)

Figure 10.13

Figure 10.14

Figure 10.15

10.4 DMA(Direct Memory Access)

• DMA controller (Figure 10.17)– Bus request– Bus grant

• Internal configuration of DMA controller (Figure 10.18)– DMA address register– DMA data register– DMA counter– DMA control register– DMA status register

10.4 DMA(continued)

• DMA transfer mode– Block transfer mode(burst mode)– Cycle stealing– Transparent mode

Figure 10.17

Figure 10.18

I/O Processors

• I/O processor (Figure 10.21)– I/O processors are sometimes called as I/O

controllers, channel controllers, or peripheral processing units(PPUs)

– I/O commands• Block transfer commands

• Control commands

• Arithmetic, logic, and branch operations

Figure 10.21

10.6 Serial Communication

• Serial communication basic– bps or baud rate– A sample transmission (Figure 10.22)– A synchronous transmission (HDLC): Figure

10.23

Figure 10.22

Figure 10.23

UART

• A computer system incorporatinf with a UART: Figure 10.24

• Internal configuration : Figure 10.25

Figure 10.24

Figure 10.25

10.7 Real World Example

• RS-232-C standard

• USB standard– USB packet formats (Figure 10.26)

Figure 10.26