Specifications

Appendix C: Registers

Flash Data Register (8383h)

This read/write register is used to access the byte in the flash memory array addressed by

the FS address registers. A read returns the value of the addressed byte if bit CDEN in the

memory control register is set; otherwise the read returns an unpredictable value. A write

to this register writes to the addressed byte if bit CDEN is set and if the flash write-protect

jumper is not installed on the board.

SRAM Data Register 8384h)

This read/write register is used to access the byte in the nonvolatile SRAM array

addressed by the FS address register. The BIOS and ROM DOS use the upper 2 KB of the

SRAM array to communicate error messages to the setup program. Thus the user should

consider the SRAM as a 30 KB array.

LED Register (8385h)

The LED register is a read/write register that controls the seven-segment display and reset

toggle switch on the front panel.

A hardware reset of the EPC-6A (not a keyboard CTRL+ALT+DEL reset) clears all of the

8130 and 8151, which may be in an undefined state. (All bits, however, are cleared by a

power-on reset.)

The above is not apparent, however, because the BIOS initialization sequence stores

values in these register fields, largely as a result of the nonvolatile configuration

information specified in the setup screen.

The BIOS clears the interrupt and event enable registers.

Flash Data Register

SRAM Data Register

LED Register

TSEN LED6 LED5 LED4 LED3 LED2 LED1 LED0

TLEDx These bits control the segments of the LED

seven-segment display as shown to the right. The

segment is lit when the corresponding bit is 0.

TSEN This bit controls both the decimal point on the LED

display and the front-panel toggle switch. When the

bit is 0, the decimal point is lit and the front-panel

switch is disabled. This bit can be used to prevent an

inadvertent reset from the front-panel switch.

LED0

LED1LED2

LED3

LED4

LED5

LED6

TSEN