revision while the '2' means the TBC implements 802.4 Revision 2. This parameter may be read via the READ VALUE command.
2.1.27 Transmitter Fault Count
The transmitter fault count is an integer in the range from zero to seven stored by the TBC in the most significant three bits. If the station sequences to the end of the token contention process and loses, or fails to pass the token to any successor, this counter is incremented by one. If this value exceeds seven, bit 1 of interrupt status word 1 will be set by the TBC (see 2.2.11 Interrupt Status Words for a complete description). This parameter may be read via the READ VALUE command.
Offset
7A TX FCNT
o
2.2 INITIALIZATION TABLE '.
C B A 1 0
o I
0I
0o I
0I
0o I
0I
0o I
0The initialization table is a 256-byte area of memory which is shared by the TBC and the host CPU. It is used by the host processor to pass operating parameters and pointers to the TBC. This is performed during the initialization sequence and whenever it is necessary to update operating parameters during TBC operation. The initialization table is also used by the TBC to pass status, statistic counters, and command return information (parameters) to the host.
The format of the initialization table is shown in Figure 2-3.
2.2.1 Private Area Function Code
Bits 0-3 of the initialization table word 0 contain the function code values that may be required by the system to access the private area. If no function codes are used, this word does not need to be initialized by the host. The TBC private area pointer is located in the subsequent two words of the initialization table.
Offset F E D C
00 10101010
2.2.2 Private Area Pointer
B A
o I
04
I
0o I
0 Private Area FCThe private area pointer is a 32-bit address which points to the 128-byte area in RAM that should only be accessed by the TBC since it contains MAC variables and parameters.
Offset F
o
C B A 402 'IM-S-B---P-riv-at-e-Ar-ea-P-oi-nte-r---H-i9-h-W-or-d---~
04 Private Area Pointer - Low Word LSB I
2.2.3 Parameters Initializing the Private Area
The parameters in displacements 08-76 are the initial values of the corresponding parameters of the private area. These values are initialized by the host CPU in the intialization table and are then loaded into the private area by the INITIALIZE command. For a detailed description of these parameters, see 2.1 TBC PRIVATE AREA.
MOTOROLA
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MC68824 USER'S MANUAL
DISPLACEMENT UPDATED
08 INITIAL HI_PRIORITY_TOKEN-HOLD_TIME Host
OA ZERO Host
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OC ZERO Host
OE INITIAL TARGEL.ROTATIDN_TIME FOR ACCESS CLASS 4 Host
10 ZERO Host
12 INITIAL TARGET-ROTATION_TIME FOR ACCESS CLASS 2 Host
14 ZERO Host
16 INITIAL TARGET-ROTATION_TIME FOR ACCESS CLASS 0 Host
18 ZERO Host
lA INITIAL TARGET-ROTATION_TIME FOR RING MAINTENANCE Host
lC INITIAL RING MAINTENANCE TIME INITIAL VALUE Host
IE INITIAL SOURCE SEGMENT/BRIDGE 10 (SID) Host
20 INITIAL TARGET SEGMENT/BRIDGE ID (TID) Host
22 INITIAL SEGMENT NUMBER MASK FOR SOURCE ROUTING Host
24 INITIAL MALINTEfLSOLlCIT_COUNT Host
26 INITIAL RX FRAME STATUS ERROR MASK Host
68 INITIAL INDIVIDUAL ADDRESS MASK - MEDIUM Host
6A INITIAL INDIVIDUAL ADDRESS MASK - HIGH Host
Figure 2-3. Initialzation Table (Sheet 1 of 2)
MC68824 USER'S MANUAL MOTOROLA
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RESPONSE DESTINATION ADDRESS POINTER Host
RESPONSE POINTER TBC
NUMBER OF NO_SUGGESSOR...8 ARGS (THRESHOLD) Host
NUMBER OF NO-SUGGESSOR...8 ARCS TBG
NUMBER OF WHOJOLLOWS TRANSMITIED (THRESHOLD) Host
NUMBER OF WHOJOLLOWS TRANSMITIED TBG
NUMBER OF TOKEN PASSES THAT FAILED (THRESHOLD) Host
NUMBER OF TOKEN PASSED THAT FAILED TBG
NUMBER OF NON_SILENCE (THRESHOLD) Host
NUMBER OF NON_SILENCE TBG
Figure 2-3. Initialzation Table (Sheet 2 of 2)
MC68824 USER'S MANUAL
2.2.4 Initial Pad Timer Preset (PTP)
The initial pad timer preset (PTP) value is used to set the length and pattern of the preamble, and the minimum number of preamble octets transmitted between frames. This register must be set
at initialization time by the host CPU according to the format shown below. The SET PTP command
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must be used after initialization to modify this register if desired. The type of physical layer used in the node determines the value to which the PTP is initialized. See 3.5.3.4 SET PAD TIMER PRESET REGISTER (PTP) for more details on the PTP.
Offset F E D C B A 9 8 7 '
78 I m I m I m I m I m I b i b I b I p i p I p i p I p p
I
pWhere:
m = Minimum number minus one of preamble octets transmitted between frames.
b = Minimum number of preamble octets minus two transmitted before frame after silence.
p = Pattern of preamble octet.
2.2.5 Initial In_Ring Desired
p
I
The initial in_ring desired parameter is a Boolean located in bit 15. A one indicates that the TBC should be a member of the token passing logical ring. After initialization the in_ring desired parameter may be modified using the SET/CLEAR IN_RING DESIRED command.
Offset D C B A
7A ~IR-'I-A-L~-o~l--o~-o~l-o~--~-o-'l-o~l--o~I--~--~I-o~--o-I~o-'I-o-'
2.2.6 Initial Address Length
The initial address length is a Boolean located in bit 14. A one indicates a 48-bit address and a zero indicates a 16-bit address. Note that the MAP specification specifies 48-bit addresses only.
Offset D C B A
7A ~1R~I-A-L~O~I--o~-o-l~o~-o~l-o~l--o~-o~1 --~o~l-o~l--o~I--~1 -o~
2.2.7 Response Destination Address Pointer
The response destination address pointer points to a frame descriptor into which the TBC writes a received RWR frame's source address in the response frame's destination address field. See 4.4 REQUEST WITH RESPONSE (RWR) TRANSMISSION for details on the RWR mechanism.
Offset D C B A
r---~
84 MSB Response Destination Address Pointer - High Word
86 Response Destination Address Pointer - Low Word LSB
2.2.8 Response Pointer
The response pointer contains a 32-bit address which points to the frame descriptor of the response to be sent when a request with response frame is received. The response pointer is used auto-matically only in predefined response mode. If the TBC is not in predefined response mode, the logical link control (LLC) must generate a response and update the response pointer. In that case,
MC68824 USER'S MANUAL MOTOROLA
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the response pointer is not valid until the RESPONSE READY command is issued to the TBC by the host. See 4.4 REQUEST WITH RESPONSE (RWR) TRANSMISSION for details on the RWR mechanism.
Offset F D C B A
88 ~IM-S-B---Re-sp-on-s-eP-o-int-er---H-ig-h-w-or-d---~
8A Response Pointer - Low Word LSB 1
2.2.9 Request with Response Pointer
The request with response (RWR) pointer contains a 32-bit address which points to the frame descriptor of the request with response frame that was received. See 4.4 REQUEST WITH RE-SPONSE (RWR) TRANSMISSION for details on the RWR mechanism.
Offset F D C B A
o
8C ~IM-S-B---Rw-R-P-o-int-er---H-ig-h-W-or-d---~
8E RWR Pointer - Low Word LSB 1
2.2.10 Command Parameter Area
The command parameter area is located in words 90 through 9C of the initialization table. This area is used to read values from, and set values into, the TBC. The command parameter area format consists of the command area and the command result area. The most frequent usage of the command parameter area is by the SET ONE WORD, SET TWO WORDS, and READ VALUE commands. For these commands, the command area is a three word area with the first word containing the parameter opcode to be set or read. The other two words contain the new parameter when setting the value of that parameter. For a description of the parameter opcodes see Tables 3-7 and 3-8. The format of the command parameter area when using other commands is defined in the specific command description in SECTION 3 COMMANDS.
Offset D C B A 9 8
90 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
92 Parameter 1 Of Needed)
94 Parameter 2 Of Needed)
4
Opcode . CPA VALO
CPA VAll
CPA VAL2
The command result area is a four word area. The first three words contain the returned value of the parameter which was requested via a READ VALUE command and the fourth word contains the status. The done bit in the status word is set by the TBC when it is finished processing any command except RESET and LOAD INITIALIZATION TABLE FC. In order to use the done bit as an indicator of command completion, it must be cleared prior to issuing the TBC a command.
The meaning of the status contained in offset 9C of the CPA is detailed under each command if used. The format of the command result area is:
MOTOROLA 2-14
MC68824 USER'S MANUAL
Offset 0 C B A
96 Parameter 1 CPA RETO
98 Parameter 2 CPA RET1
9A Parameter 3 CPA RET2
9C Status
I Do~e
Bit
2.2.11 Interrupt Status Words
Interrupt status bits are updated continuously by the TBC as status changes. To change a status bit, the TBC reads the appropriate word of the status area, updates the proper bit, and then writes the word back to the memory area. If the corresponding status bit is already set, then no action is taken by the TBC. The interrupt status word, combined with the interrupt status mask, determines whether an interrupt will be generated. If a special event occurs and the corresponding bit in the interrupt mask is zero, then an interrupt request will not be generated; however, the corresponding status bit will be set to one. If a special event occurs and the corresponding bit in the interrupt mask is one, then an interrupt will be generated, and the corresponding status bit will be set to one. To clear the interrupt status words, the CLEAR INTERRUPT STATUS command must be issued.
2.2.11.1 INTERRUPT STATUS WORD O. The format of interrupt status word 0 is shown below:
Offset F E D C B A 9 8 7 6 5 4 3 2 1 0