Hayes Microcomputer Products RCV56HCF manual Command Register, Status Register, Bit Description

RCV56HCF PCI/CardBus Modem Designer’s Guide

5.1.3 Command Register

The Command Register bits are described in Table 5-2.

	Table 5-2. Command Register
Bit	Description
0	Controls a device’s response to I/O Space accesses. A value of 0 disables the device response. A value of
	1 allows the device to respond to I/O Space accesses. State after RST# is 0.
1	Controls a device’s response to Memory Space accesses. A value of 0 disables the device response. A
	value of 1 allows the device to respond to Memory Space accesses. State after RST# is 0.
2	Controls a device’s ability to act as a master on the PCI bus. A value of 0 disables the device from
	generating PCI accesses. A value of 1 allows the device to behave as a bus master. State after RST# is 0.
3	Not Implemented.
4	Not Implemented.
5	Not Implemented.
6	This bit controls the device’s response to parity errors. When the bit is set, the device must take its normal
	action when a parity error is detected. When the bit is 0, the device must ignore any parity errors that it
	detects and continue normal operation. This bit’s state after RST# is 0.
7	This bit is used to control whether or not a device does address/data stepping. This bit is read only from the
	PCI interface. It is loaded from the serial EEPROM after RST#.
8	This bit is an enable bit for the SERR# driver. A value of 0 disables the SERR# driver. A value of 1 enables
	the SERR# driver. This bit’s state after RST# is 0.
9	This bit controls whether or not a master can do fast back-to-back transactions to different devices. A value
	of 1 means the master is allowed to generate fast back-to-back transactions to different agents as described
	in Section 3.4.2 of the PCI 2.1 specification. A value of 0 means fast back-to-back transactions are only
	allowed to the same agent. This bit’s state after RST# is 0.
10-15	Reserved

5.1.4 Status Register

The Status Register bits are described in Table 5-3.

Status register bits may be cleared by writing a ‘1’ in the bit position corresponding to the bit position to be cleared. It isnot possible to set a status register bit by writing from the PCI Bus. Writing a ‘0’ has no effect in any bit position.

	Table 5-3. Status Register
Bit	Description
0-4	Reserved
5	Not Implemented.
6	Not Implemented.
7	Not Implemented.
8	This bit is only implemented by bus masters. It is set when three conditions are met: 1) the bus agent
	asserted PERR# itself or observed PERR# asserted; 2) the agent setting the bit acted as the bus master for
	the operation in which the error occurred; and 3) the Parity Error Response bit (Command Register) is set.
9-10	These bits encode the timing of DEVSEL#. These are encoded as 00 for fast, 01 for medium, and 10 for slow
	(11 is reserved.) These bits are read-only and must indicate the slowest time that a device asserts DEVSEL#
	for any bus command except Configuration Read and Configuration Write.
11	Not Implemented.
12	This bit must be set by a master device whenever its transaction is terminated with Target-Abort. All master
	devices must implement this bit.
13	This bit must be set by a master device whenever its transaction (except for Special Cycle) is terminated with
	Master-Abort. All master devices must implement this bit.
14	This bit must be set whenever the device asserts SERR#. Devices which will never assert SERR# do not
	need to implement this bit.
15	This bit must be set by the device whenever it detects a parity error, even if parity error handling is disabled
	(as controlled by bit 6 in the Command register).

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