Computer I/O Synchronization Quiz

Data Transfer Methods

• Flags synchronize timing differences between I/O devices and the computer.
• FGI (Input flag) starts at 0, indicating the INPR register is ready but empty.
• FGO (Output flag) starts at 1, which means the OUTR register is ready to receive data from the AC but is currently empty.

Program Controlled Input/Output

• Input operations involve looping until data is ready, using instructions like SKI (Skip if Input) and INP (Input).
• Output processes use similar looping with SKO (Skip if Output) and OUT (Output).
• Advantages of program-controlled I/O include simplicity and minimal hardware requirement, while it involves continuous CPU engagement, slowing down performance to I/O speeds.

Interrupt Initiated Input/Output

• Communication occurs only when data needs to be transferred, prompting an interrupt.
• The I/O interface monitors the device readiness, generating an interrupt request to the CPU.
• Upon interrupt detection, the CPU pauses its current task to service the interrupt before resuming its prior operation.
• IEN (Interrupt-enable flip-flop) can be set/cleared to control interrupt capabilities.

Interrupt Cycle

• Functions as a hardware implementation of branching and saving the return address for tasks.
• The process repeatedly fetches instructions from memory, executing cycles based on the type of instruction detected.

Fetch and Decode Process

• PC (Program Counter) is initially loaded with the first instruction's address, while the SC (State Counter) is cleared.
• Post each clock pulse, the SC increments to facilitate instruction execution.

Instruction Types

• Register Reference Instructions: Identified by specific bits in the instruction; execution begins with a timing signal.
• Memory Reference Instructions: Utilize addresses stored in AR and depend on memory cycles to complete in one CPU cycle. They initiate processing signals T2 and T3.

Memory Reference Operations

• AND operation stores the result in AC after reading from the memory address.
• ADD operation adds the operand from memory to AC, also tracking carry-out.
• LDA (Load to AC), STA (Store AC), BUN (Branch Unconditionally), BSA (Branch and Save Address), and ISZ (Increment and Skip if Zero) provide various control flows and data management mechanisms.

Input-Output and Interrupt Configuration

• Input and Output registers are 8 bits long with flags for monitoring state.
• Serial data is managed via INPR and OUTR registers, communicating with processing and output devices.

Basic Computer Organization

• Comprises a processor and memory capable of storing 4096 words, with each word being 16 bits in length.
• Instructions are sequences leading to operation execution in the CPU, involving a systematic fetch and decode mechanism.

Instruction Format and Addressing

• Instructions consist of an opcode for the operation and an address for the operands.
• Effective address (EA) is directly usable for operand access.
• Addressing can be direct or indirect, depending on how the instruction points to data.

Processor Registers

• PC tracks the next instruction address using 12 bits.
• AR indicates current addressing of memory locations.
• DR holds operands found in memory, while the accumulator (AC) serves as a general-purpose register integral for operations.

Test your understanding of program-controlled data transfer and the flags used for synchronizing I/O device timing with the computer. This quiz explores the initial conditions of input and output registers and their roles in data transfer. Dive into the mechanics of how computers communicate with peripheral devices.