Intel mcs-48 manual Command Descriptions, Read Data

inter8272

TABLE 2. COMMAND MNEMONICS

SYMBOL	NAME	DESCRIPTION
Ao	Address Line 0	AO controls selection of Main Status
		Register (AO= 0) or Data Register (AO =1).
C	Cylinder Number	C stands for the current selected Cylinder
		track number 0 through 76 of the medium.
0	Data	o stands for the data pattern which Is
		going to be written Into a Sector.
orOo	Data Bus	B-blt Data Bus where 07 is the most
		significant bit, and 00 Is the least signlfl'
		cant bit.
OSO,OS1	Drive Select	OS stands tor a selected drive number 0
		or 1.
oTl	Data length	When N is defined as OQ, DTl stands for
		the data length which users are going to
		read out or write into the Sector.

SYMBOL	NAME	DESCRIPTION
NCN	New Cylinder Number	NCN stands for a new Cylinder number,
		which Is going to be reached as a result
		of the Seek operation, Desired position of
		Head.
NO	Non·DMA Mode	NO stands for operation In the Non·DMA
		Mode,
PCN	Present Cylinder	PCN stands for the Cylinder number at
	Number	the completion of SENSE INTERRUPT
		STATUS Command. Position of Head at
		present time.
R	Record	R stands for the Sector number, which
		will be read or written.
R/W	Read/Write	R/W stands for either Read (R) or Write
		(IN) aignal.

EOT	End of Track	EOT stands for the final Sector number of
		a Cylinder.
GPl	Gap Length	GPL stands for the length of Gap 3
		(spacing between Sectors excluding VCO
		Sync Field).
H	Head Address	H stands for head number 0 or 1, as
		specified in 10 field.
HOS	Head Select	HOS stands for a selected Mad number 0
		or 1 (H = HOS in all command words).
HLT	Head Load Time	HLT stands for the head load time in the
		FOO (2 to 254 ms in 2 ms increments).
HUT	Head Unload Time	HUT stands for the head unload time after
		a read or write operation has occurred (16
		to 240ms in 16ms Increments).
MFM	FM or MFM Mode	If MF is low, FM mode is selected and If
		It Is high, MFM mode Is selected,
MT	Multi·Track	If MT is high, a multi·trackoperation is to

SC Sector

SK Skip

SRT Step Rate Time

STO	Status 0
ST 1	Status 1
ST 2	Status 2
ST 3	Status 3

SC Indicates the number of Sectors per Cylinder.

SK stands for Skip Deleted Data Address Mark.

SRT stands for the Stepping Rate for the FDD (1 to 16ms In 1 ms Increments). Stepping Rate applies to a1\ drives

(F = 1 ms, E= 2 ms, etc.).

ST 0-3 stand for one of four registers which store the status information after a command has been executed. This information 15 available during the result phase after command execution. These registers should not be confused with the main status register (selected by AO = 0). ST 0-3 may be read only after a command has been executed and contain information relevant to that particular command.

		be performed (a cylinder under both HDO
		and HD1 will be read or written).
N	Number	N stands for the number of data bytes
		written in a Sector.

STP	During a Scan operation, If STP= 1, the
	data in contiguous sectors Is compared
	byte by byte with data sent from the
	processor (or DMA), and if STP= 2, then
	alternate sectors are read and compared.

COMMAND DESCRIPTIONS

During the Command Phase, the Main Status Register must be polled by the CPU before each byte is written into the Data Register. The 010 (OB6) and ROM (OB7) bits in the Main Status Register must be in the "0" and "1" states respectively, before each byte of the com- mand may be written into.the 8272. The beginning of the execution phase for any of these commands will cause 010 and ROM to switch to "1" and "0" states respective- ly.

READ DATA

A set of nine (9) byte words are required to place the FOC into the Read Data Mode. After the Read Data com· mand has been issued the FOC loads the head (if it is in the unloaded state), waits the specified head settling time (defined in the Specify Command), and begins reading 10 Address Marks and 10 fields. When the cur· rent sector number ("R") stored in the 10 Register (lOR)

compares with the sector number read off the diskette, then the FOC outputs data (from the data field) byte-bY- byte to the main system via the data bus.

After completion of the read operation from the current sector, the Sector Number is incremented by one, and the data from the next sector is read and output on the data bus. This continuous read function is called a "Multi·Sector Read Operation." The Read Data Com- mand may be terminated by the receipt of a Terminal Count signal. Upon receipt of this signal, the FOC stops outputting data to the processor, but will continue to read data from the current sector, check CRC (Cyclic Redundancy Count) bytes, and then at the end of the sector terminate the Read Data Command.

The amount of data which can be handled with a Single command to the FOC depends upon MT (multi·track), MFM (MFM/FM), and N (Number of Bytes/Sector). Table 3 below shows the Transfer Capacity.

TABLE 3. TRANSFER CAPACITY

Multl·Track	MFM/FM	Bytes/Sector	Maximum Transfer Capacity			Final Sector Read
MT	MFM	N	(BytesJSector)(Number of Sectors)			from Diskette
0	0	00	(128) (26) =		3.328	26 at Side 0
0	1	01	(256)(26) =		8,656	or 26 at Side 1
1	0	00	(128) (52)=		6,656	26 at Side 1
1	1	01	(256) (52) = 13,312
0	0	01	(256)(15)=		3,840	15 at Side 0
0	1	02	(512)(15)=		7,680	or 15 at Side 1
1	0	01	(256) (30)=		7,680	15 at Side 1
1	1	02	(512) (30)= 15,360
0	0	02	(512) (8)	=	4.096	8 at Side 0
0	1	03	(1024) (8)	=	8,192	or 8 at Side 1
1	0	02	(512)(16)=		8,192	8 at Side 1
1	1	03	(1024)(16)=		16,384

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