Intel mcs-48 manual Write Deleted Data, Read Deleted Data, Read a Track, Readid, Format a Track

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•Head Unload Time Interval

•10 Information when the processor terminates com- mand (see Table 2)

•Definition of DTL when N =0 and when N#-O

In the Write Data mode, data transfers between the proc- essor and FDC must occur every 31 I'sin the FM mode, and every 15 I'sin the MFM mode. If the time interval between data transfers Is longer than this then the FDC sets the OR (Over Run) flag In Status Register 1 to a 1 (high), and terminates the Write Data Command.

WRITE DELETED DATA

This command is the same as the Write Data Command except a Deleted Data Address Mark is written at the beginning of the Data Field instead of the normal Data Address Mark.

READ DELETED DATA

This command is the same as the Read Data Command except that when the FDC detects a Data Address Mark at the beginning of a Data Field (and SK =0 (low)), It will read all the data in the sector and set the CM flag in Status Register 2 to a 1 (high), and then terminate the command. If SK =1, then the FDC skips the sector with the Data Address Mark and reads the next sector.

READ A TRACK

This command is similar to READ DATA Command except that the entire data field is read continuously from each of the sectors of a track. Immediately after encountering the INDEX HOLE, the FDC starts reading all data fields on the track as continuous blocks of data. If the FDC finds an error in the 10 or DATA CRC check bytes, it continues to read data from the track. The FDC compares the 10 information read from each sector with the value stored In the lOR, and sets the NO flag of Status Register 1 to a 1 (high) If there is no comparison. Multi-track or skip operations are not allowed with this command.

This command terminates when EOT number of sectors have been read. If the FDC does not find an 10 Address Mark on the diskette after it encounters the INDEX HOLE for the second time, then it sets the MA (missing address mark) flag in Status Register 1 to a 1 (high), and terminates the command. (Status Register 0 has bits 7 and 6 set to 0 and 1 respectively.)

READID

The READ 10 Command is used to give the present posi- tion of the recording head. The FDC stores the values from the first 10 Field it is able to read. If no proper 10 Address Mark is found on the diskette, before the IN- DEX HOLE is encountered for the second time then the MA (Missing Address Mark) flag in Status Register 1 Is set to a 1 (high), and if no data Is found then the NO (No Data) flag Is also set in Status Register 1 to a 1 (high) and the command is terminated.

FORMAT A TRACK

The Format Command allows an entire track to be for- matted. After the INDEX HOLE Is detected, Data is writ- ten on the Diskette: Gaps, Address Marks, 10 Fields and Data Fields, all per the IBM System 34 (Double Density) or System 3740 (Single Density) Format are recorded. The particular format which will be written Is controlled by the values programmed into N (number of bytes/sec- tor), SC (sectors/cylinder), GPL (Gap Length), and 0 (Data Pattern) which are supplied by the processor dur- ing the Command Phase. The Data Field Is filled with the Byte of data stored in D. The 10 Field for each sector is supplied by the processor; that is, four data requests per sector are made by the FDC for C (Cylinder Number), H (Head Number), R (Sector Number) and N (Number of Bytes/Sector). This allows the diskette to be formatted with nonsequential sector numbers, if desired.

After formatting each sector, the processor must send new values for C, H, R, and N to the 8272 for each sector on the track. The contents of the R register is In- cremented by one after each sector is formatted, thus, the R register contains a value of R + 1 when It Is read during the Result Phase. This incrementing and format- ting continues for the whole track until the FDC en- counters the INDEX HOLE for the second time, where- upon it terminates the command.

If a FAULT signal is received from the FDD at the end of a write operation, then the FDC sets the EC flag of Status Register 0 to a 1 (high), and terminates the com- mand after setting bits 7 and 6 of Status Register 0 to 0 and 1 respectively. Also the loss of a READY signal at the beginning of a command execution phase causes command termination.

Table 5 shows the relationship between N, SC, and GPL for various sector sizes:

TABLE 5. SECTOR SIZE RELATIONSHIPS

FORMAT	SECTOR SIZE	N	SC	GPL'	GPL2	REMARKS
	128 bytes/Sector	00	1,,-{16)	07(16)	18(16)	IBM Diskette 1
FM Mode	256	01	OF(16)	OE(16)	2A(16)	IBM Diskette 2
	512	02	06	1B(16)	3,,-{16)
	1024 bytes/Sector	03	04	-	-
FM Mode	2046	04	02	-	-
	4096	05	01	-	-

25601 1A(16) O~16) 36(16) IBM Diskette 20

51202 OF(16) 1B(16) 54(16)

MFM Mode	1024	03	06	35(16)	74(16) IBM Diskette 20
	2048	04	04	-	-
	4096	05	02	-	-
	8192	08	01	-	-

Note: 1. Suggested val~es of GPL in Read or Write Commands to avoid splice point between data field and 10 field of contiguous sections.

2. Suggested values of GPL in format command,

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