Pinout Diagram: IC 8279, IC 8255, IC 8251, IC 8259, IC 8253, IC 8237
IC 8279 Pinout Diagram
Here, in the below figure, you can see the pinout diagram of IC 8279
The IC 8279 is a versatile interface Integrated Circuit that can handle both keyboard scanning (up to 64 keys, with debounce and FIFO buffering) and display driving (16‑digit capability). It is used to reduce the CPU’s workload by managing low‑level scanning, refresh, and interrupt-driven data handling.
The 8279 IC has 40 pins housed in a DIP package. Here, is the below pin descriptions,
Pin 1-2, 5-7, 38-39 (RL0–RL7): Keyboard return lines (detect key presses).
Pin 3 (CLK): Clock input for internal timing.
Pin 4 (IRQ): Interrupt request output to CPU.
Pin 9 (RESET): Resets the 8279.
Pin 10 (RD): Read signal (active low).
Pin 11 (WR): Write signal (active low).
Pin 12–19 (DB0–DB7): Bidirectional data bus.
Pin 20 (VSS): Ground.
Pin 21 (A0): Address line (command/data select).
Pin 22 (CS): Chip select (active low).
Pin 23–26 (SL0–SL3): Scan lines for keyboard/display multiplexing.
Pin 27–24 (OUT A3–A0): Display output lines (part A).
Pin 28–31 (OUT B0–B3): Display output lines (part B).
Pin 36 (SHIFT): Shift key input.
Pin 37 (CNTL/STB): Control input or strobe (mode-dependent).
Pin 40 (VCC): +5V power supply.
IC 8255 Pinout Diagram
Here, in the below figure, you can see the pinout diagram of IC 8255
The IC 8255 is a Programmable Peripheral Interface (PPI) Integrated Circuit used to connect I/O devices (like keyboards, displays, etc.) to a microprocessor. It has three 8-bit ports: Port A, Port B, and Port C, which can be configured individually as input or output. Port C can also be split into two 4-bit ports. The 8255 operates in three modes such as Mode 0 (basic I/O), Mode 1 (strobed I/O with handshaking), and Mode 2 (bidirectional bus). It allows flexible I/O handling without burdening the CPU that is why it is widely used in embedded and microprocessor systems.
Here is the pinout description,
Pins 1–4, 37–40 (PA0–PA7): Port A I/O lines – 8-bit bidirectional data lines.
Pins 18–25 (PB0–PB7): Port B I/O lines – 8-bit bidirectional.
Pins 10–17 (PC0–PC7): Port C I/O lines – 8-bit bidirectional, divided into upper (PC4–PC7) and lower (PC0–PC3) nibbles.
Pin 5 (RD): Read – active low: enables the 8255 to send data/status to the CPU.
Pin 6 (CS): Chip Select – active low: enables chip for operations.
Pin 8 (A1): Address input – selects ports/control register.
Pin 9 (A0): Address input – along with A1 selects target register.
Pins 27–34 (D0–D7): Data bus – bidirectional lines for data/control-word transfer.
Pin 35 (RESET): Reset input – active high; clears control register and sets all ports to input mode.
Pin 36 (WR): Write – active low: enables writing data/control word to the 8255.
Pin 26 (VCC) and Pin 7 (GND): Power supply pins – +5V and ground, respectively.
IC 8251 Pinout Diagram
Here, in the below figure, you can see the pinout diagram of IC 8251
The IC 8251 is a Programmable Communication Interface used for serial data communication. It acts as a Universal Synchronous/Asynchronous Receiver/Transmitter (USART) which allows a microprocessor to communicate over serial lines. The 8251 can operate in both synchronous and asynchronous modes and supports full-duplex communication. It includes separate buffers for transmission and reception, handles baud rate control, parity, stop bits, and error detection, and reduces the CPU's workload by managing the serial data flow. It is commonly used for interfacing modems, serial terminals, and other serial devices.
Here is the below pinout description,
Pins 1–2 (D2, D3), Pin 5 (D4), Pin 6 (D5), Pin 7 (D6), Pin 8 (D7), and Pins 27–28 (D0, D1): Data bus lines for parallel data transfer between CPU and USART.
Pin 3 (RX): Serial data input (Receive Data).
Pin 9 (TXC): Transmit Clock input (active low); controls data transmission rate.
Pin 10 (WR): Write control (active low) for sending data/commands to the USART.
Pin 11 (CS): Chip Select (active low); enables the USART for operations.
Pin 12 (C/D): Command/Data select; distinguishes between accessing control/status vs data registers.
Pin 13 (RD): Read control (active low) for reading data/status from the USART.
Pin 14 (RXRDY): Receiver Ready – indicates received character is ready to be read by the CPU.
Pin 15 (TXRDY): Transmitter Ready – indicates the USART is ready to accept new data from the CPU.
Pin 16 (SYNDET/BD): Sync Detect (synchronous mode) or Break Detect (asynchronous mode).
Pin 17 (CTS): Clear To Send (active low) – modem control input.
Pin 18 (TXEMPTY): Transmitter Empty – indicates both buffer and shift register are empty.
Pin 19 (TXD): Serial Transmit Data output.
Pin 20 (CLK): System Clock input for the USART.
Pin 21 (RESET): Reset input; initializes the device.
Pin 22 (DSR): Data Set Ready (active low) – modem control input.
Pin 23 (RTS): Request To Send (active low) – modem control output.
Pin 24 (DTR): Data Terminal Ready (active low) – modem control output.
Pin 25 (RXC): Receive Clock input (active low) – controls data reception rate.
Pin 26 (VCC): +V power supply.
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IC 8259 Pinout Diagram
Here, in the below figure, you can see the pinout diagram of IC 8259
The IC 8259 is a Programmable Interrupt Controller (PIC) designed to handle multiple hardware interrupts for a microprocessor system. It can manage up to 8 interrupt inputs and can be cascaded with other 8259s to support up to 64 interrupts. It prioritizes interrupts, sends interrupt signals to the CPU, and provides the appropriate interrupt vector address during acknowledgment.
Here is the pinout description,
Pin 1 – CS: Chip Select – enables the 8259 for communication (active low).
Pin 2 – WR: Write – writes command or data (active low).
Pin 3 – RD: Read – reads status or data (active low).
Pins 4–11 – D7–D0: 8-bit bidirectional data bus.
Pin 12 – CAS0: Cascade line for identifying slave PICs.
Pin 13 – CAS1: Cascade line.
Pin 14 – GND: Ground.
Pin 15 – CAS2: Cascade line.
Pin 16 – SP/EN: Selects Master/Slave mode or enables buffer (depends on mode).
Pin 17 – INT: Interrupt Output to CPU.
Pins 18–25 – IR0 to IR7: Interrupt Request Inputs from peripherals.
Pin 26 – INTA: Interrupt Acknowledge from CPU (active low).
Pin 27 – A0: Address line for internal register selection.
Pin 28 – VCC: +5V power supply.
IC 8253 Pinout Diagram
Here, in the below figure, you can see the pinout diagram of IC 8253
The Intel 8253 is a Programmable Interval Timer (PIT) widely used alongside Intel microprocessors (like 8085, later in PCs). It has inbuilt three independent 16-bit down counters, each with its own clock (CLK), gate input (GATE), and output (OUT) pin. These counters can operate in various modes (monostable, rate generation, square wave, etc.) to perform timing tasks, generate interrupts, refresh DRAM, or drive audio.
Here, is the pinout description.
Pins 1–8 – D7-D0: 8-bit bidirectional data bus for communication with CPU.
Pin 9 – CLK0: Clock input for Counter 0.
Pin 10 – OUT0: Output signal from Counter 0.
Pin 11 – GATE0: Gate input for Counter 0—enables or controls counting.
Pin 12 – GND: Ground (0V reference).
Pin 13 – OUT1: Output from Counter 1.
Pin 14 – GATE1: Gate input for Counter 1.
Pin 15 – CLK1: Clock input for Counter 1.
Pin 16 – GATE2: Gate input for Counter 2.
Pin 17 – OUT2: Output from Counter 2.
Pin 18 – CLK2: Clock input for Counter 2.
Pin 19 – A0: Address line—selects between counters and control word register.
Pin 20 – A1: Address line—works with A0 for selecting registers.
Pin 21 – CS: Chip Select (active low)—enables device for read/write operations.
Pin 22 – RD: Read control (active low)—CPU reads data from 8253.
Pin 23 – WR: Write control (active low)—CPU writes data or control word.
Pin 24 – VCC: +5 V power supply.
IC 8237 Pinout Diagram
Here, in the below figure, you can see the pinout diagram of IC 8237
The Intel 8237 is a four-channel Direct Memory Access (DMA) controller designed to facilitate high-speed data transfers between memory and I/O devices without burdening the CPU. Operating in systems with processors like the 8086/8088, it handles transfers up to 1.6 MB/s. The chip supports various transfer modes—single, block, demand, memory-to-memory, etc.
Here, is the pinout description,
Pin 1 – IOR: I/O Read – used during DMA write or programming operations.
Pin 2 – IOW: I/O Write – used during DMA read or programming.
Pin 3 – MEMR: Memory Read – controls reading from memory during DMA.
Pin 4 – MEMW: Memory Write – controls writing to memory during DMA.
Pin 6 – READY: Wait-state insertion signal for slow components.
Pin 7 – HLDA: Hold Acknowledge – from CPU to signal bus control release.
Pin 9 – AEN: Address Enable – enables upper address latch and disables bus buffers during DMA.
Pin 10 – HRQ: Hold Request – DMA controller requests CPU control of the bus.
Pins 12–13, 15: CLK (Pin 12): Clock input for DMA timing. RESET (Pin 13): Initializes registers, masks, flip-flops.
Pins 14–17: DACK2 (Pin 14), DACK3 (Pin 15): DMA acknowledge outputs for channels 2 and 3. DREQ3 (Pin 16), DREQ2 (Pin 17): DMA request inputs for channels 3 and 2.
Pins 18–19: DREQ1 (Pin 18), DREQ0 (Pin 19), DMA request inputs for channels 1 and 0.
Pin 20 – VSS: Ground.
Pins 21–30: DB7–DB0: Bidirectional data bus for transfers and programming logic. The order is: DB7 (Pin 21) through DB0 (Pin 30).
DACK1 (Pin 24) and DACK0 (Pin 25): DMA acknowledges for channels 1 and 0.
Pin 31 – VCC: +5 V power supply.
Pins 32–35(A0-A3): Address lines for selecting internal registers during programming and for providing the lower bits of the DMA transfer address.
Pin 36(EOP): End of Process – signals completion of a DMA cycle.
Pins 37–40(A4-A7): Outputs for the upper DMA address bits during transfers.
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