RX211 floppy disk controller

The RX211 and RXV21 are controllers for the RX02 )and also the RX01) floppy disk drives for the UNIBUS and QBUS, respectively.

They have an identical programming interface; both use DMA to transfer information between main memory and the floppy.

Device registers

Register	Abbreviation	Address
Command and Status Register	RX2CS	777170
Data Buffer Register	RX2DB	777172

777170: Command and Status Register (RX2CS)

Error	Initialize	Extended Address		RX02	Unused		Density	Transfer Request	Interrupt Enable	Done	Unit Select	Function			Go
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

The function codes are:

Code	Function
0	Fill Buffer
1	Empty Buffer
2	Write Sector
3	Read Sector
4	Set Media Density
5	Read Status
6	Write Deleted Data Sector
7	Read Error Register

777172: Data Buffer Register (RX2DB)

This register contains one of several 'virtual' registers, depending on the function in progress.

The 'Transfer Request' bit in the RXCS is used to indicate which virtual register is in use at any given time.

Track Address (RX2TA)

Unused								0	Track
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Sector Address (RX2SA)

Unused								0	0	0	Sector
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Word Count (RX2WC)

Unused								0	Count
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Bus Address (RX2BA)

Address
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Data Buffer (RX2DB)

Unused								Data
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Note the name clash between this virtual register, and the actual register which contains it.

Error and Status (RX2ES)

Unused				NXM	WC Overflow	Reserved	Unit Select	Drive Ready	Deleted Data	Drive Density	Density Error	AC Low	Initialize Done	Reserved	CRC Error
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Error (RX2ER)

Unused								Error Code
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Error code values:

Value	Meaning
0010	Drive 0 failed to see home on Initialize
0020	Drive 1 failed to see home on Initialize
0040	Tried to access a track greater than 76
0050	Home was found before desired track was reached
0070	Desired sector could not be found after looking at 52 headers (2 revolutions)
0110	More than 40 μsec and no SEP clock seen
0120	A preamble could not be found
0130	Preamble found but no ID mark found within allowable time span
0140	CRC error found on what we thought was a header
0150	The header track address of a good header does not compare with the desired track
0160	Too many tries for an IDAM (identifies header)
0170	Data AM not found in allotted time
0200	CRC error on reading the sector from the disk
0220	R/W electronics failed maintenance test mode
0230	Word count overflow
0240	Density error
0250	Wrong key word for set media density command