01-08-2012, 12:34 PM
Systems Design and Programming
Systems Design & Programming.pdf (Size: 217.18 KB / Downloads: 38)
CS: Chip select that enables programming, reading the keyboard, etc.
DB7-DB0: Consists of bidirectional pins that connect to data bus on micro.
IRQ: Interrupt request, becomes 1 when a key is pressed, data is available.
OUT A3-A0/B3-B0: Outputs that sends data to the most significant/least significant
nibble of display.
RD(WR): Connects to micro's IORC or RD signal, reads data/status registers.
RESET: Connects to system RESET.
RL7-RL0: Return lines are inputs used to sense key depression in the keyboard matrix.
Shift: Shift connects to Shift key on keyboard.
SL3-SL0: Scan line outputs scan both the keyboard and displays.
8254 Pin Definitions
A1, A0:The address inputs select one of the four internal
registers with the 8254 as follows:
CLK: The clock input is the timing source for each of the
internal counters.
It is often connected to the PCLK signal from the
bus controller.
CS: Chip Select enables the 8254 for programming, and reading and writing.
G: The gate input controls the operation of the counter in some modes.
OUT: A counter output is where the wave-form generated by the timer is available.
RD/WR: Read/Write causes data to be read/written from the 8254 and often connects to the
IORC/IOWC.