RX11 floppy disk controller

The RX11 and RXV11 are controllers for the RX01 floppy disk drives for the UNIBUS and QBUS.

They have an identical programming interface; both use programmed I/O. The controller contains a buffer, which is filled or emptied under program control.

Device registers

Register	Abbreviation	Address
Command and Status Register	RXCS	777170
Data Buffer Register	RxDB	777172

777170: Command and Status Register (RXCS)

Error	Initialize	Unused						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

Setting the 'Initialize' bit does not clear the 'Interrupt Enable' bit on the RXV11.

The function codes are:

Code	Function
0	Fill Buffer
1	Empty Buffer
2	Write Sector
3	Read Sector
4	Not used
5	Read Status
6	Write Deleted Data Sector
7	Read Error Register

777172: Data Buffer Register (RXDB)

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 (RXTA)

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

Sector Address (RXSA)

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

Data Buffer (RXDB)

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 (RXES)

Unused								Drive Ready	Deleted Data	Unused			Initialize Done	Parity Error	CRC Error
15	14	13	12	11	10	09	08	07	06	05	04	03	02	01	00

Error (RXER)

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
0030	Found home when stepping out 10 tracks for INIT
0040	Tried to access a track greater than 77
0050	Home was found before desired track was reached
0060	Self-diagnostic error
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 I/O 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
0210	All parity errors

External links

• RX11 Floppy Disk System Option Bulletin
• RX8/RX11 floppy disk system user's manual (EK-RX01-0P-001)
• RX8/RX11 floppy disk system maintenance manual (EK-RX01-MM-002)
• RXV11 user's manual (EK-RXV11-OP-002)
• RX01/RX02 8" floppy disk drive RX11/RX211 controller