Rainbow Electronics AT76C551 User Manual

Page 69

AT76C551

1612D–08/01

US_MCC: Modem Control Register

addr: 700030 hex

R/W

8 bits

• Bit 7 – Reserved

• Bit 6 – LB RI Value

The compliment of the value of RI input, when Modem Control Loop Back mode is enabled.

• Bit 5 – LB CD Value

The compliment of the value of CD input, when Modem Control Loop Back mode is enabled.

• Bit 4 – MC LB EN: Modem Control Loop Back Mode Enable

• Bit 3 – DSR Change Mask

This bit when set enables the DSR change interrupt. If the DSR change bit of Modem Control
Input Register US_MCI is set, then an interrupt will occur.

• Bit 2 – RI Change Mask

This bit when set enables the RI change interrupt. If the RI change bit of Modem Control Input
Register US_MCI is set, then an interrupt will occur.

• Bit 1 – CD Change Mask

This bit when set enables the CD change interrupt. If the CD change bit of Modem Control
Input Register US_MCI is set, then an interrupt will occur.

• Bit 0 – CTS Change Mask

This bit when set enables the CTS change interrupt. If the CTS change bit of Modem Control
Input Register US_MCI is set, then an interrupt will occur.

Note:

Default Value: 00 hex

The low nibble of the Modem-control register is the Modem Control interrupt mask register
(see US_MCI).

Note:

US_IER cannot control the interrupts from modem control logic.

The high nibble is used to control the Modem Control Loop-back mode. If MC Loop Back
enable bit is set, then the US_MCC bits 5 - 6 control the values of CD and RI inputs (see and
US_MCI bits 5 - 6 and 1 - 2).

When MC Loop-back mode is enabled, then input pins RI, CD, DSR, CTS are assigned the
following values:

bit 6 of register US_MCC (inverted)

bit 5 of register US_MCC (inverted)

DSR

pin DTR

CTS

pin RTS