COM20019I_06 Datasheet, PDF (23/65 Pages) SMSC Corporation – Low Cost ARCNET (ANSI 878.1) Controller with 2K x 8 On-Board RAM

Low Cost ARCNET (ANSI 878.1) Controller with 2K x 8 On-Board RAM
Chapter 6 FUNCTIONAL DESCRIPTION
6.1 MICROSEQUENCER
The COM20019I contains an internal microsequencer which performs all of the control operations
necessary to carry out the ARCNET protocol. It consists of a clock generator, a 544 x 8 ROM, a program
counter, two instruction registers, an instruction decoder, a no-op generator, jump logic, and
reconfiguration logic.
The COM20019I derives a 625 kHz and a 312.5 kHz clock from the output clock of the Clock Multiplier.
These clocks provide the rate at which the instructions are executed within the COM20019I. The 625 kHz
clock is the rate at which the program counter operates, while the 312.5 kHz clock is the rate at which the
instructions are executed. The microprogram
is stored in the ROM and the instructions are fetched and then placed into the instruction registers. One
register holds the opcode, while the other holds the immediate data. Once the instruction is fetched, it is
decoded by the internal instruction decoder, at which point the COM20019I proceeds to execute the
instruction. When a no-op instruction is encountered, the microsequencer enters a timed loop and the
program counter is temporarily stopped until the loop is complete. When a jump instruction is encountered,
the program counter is loaded with the jump address from the ROM. The COM20019I contains an internal
reconfiguration timer which interrupts the microsequencer if it has timed out. At this point the program
counter is cleared and the MYRECON bit of the Diagnostic Status Register is set.
REGISTER
STATUS
MSB
RI/TRI
DIAG.
STATUS
ADDRESS
PTR HIGH
ADDRESS
PTR LOW
DATA
SUB ADR
MY-
RECON
RD-
DATA
A7
D7
X
CONFIG-
URATION
TENTID
NODE ID
SETUP1
NEXT ID
RESET
TID7
NID7
P1
MODE
NXT ID7
SETUP2
RBUS-
TMG
X/RI
DUPID
AUTO-
INC
A6
D6
X
CCHEN
TID6
NID6
FOUR
NAKS
NXT ID6
X
Table 6.1 - Read Register Summary
X/TA
READ
POR
TEST
RECON
TMA
RCV-
ACT
X
TOKEN
X
EXC-
NAK
X
TENTID
A10
NEW
NEXTID
A9
LSB
TA/
TTA
X
A8
A5
A4
A3
A2
A1
A0
D5
X
TXEN
TID5
NID5
X
NXT ID5
X
D4
X
ET1
TID4
NID4
RCV-
ALL
NXT ID4
X
D3
X
ET2
TID3
NID3
CKP3
NXT ID3
EF
D2
D1
SUB-AD2 SUB-AD1
BACK-
PLANE
TID2
NID2
CKP2
SUB-AD1
TID1
NID1
CKP1
NXT
ID2
NO-
SYNC
NXT ID1
RCN-
TM1
D0
SUB-
AD0
SUB-
AD0
TID0
NID0
SLOW-
ARB
NXT
ID0
RCM-
TM2
ADDR
00
01
02
03
04
05
06
07-0
07-1
07-2
07-3
07-4
SMSC COM20019I
Page 23
DATASHEET
Rev. 03-07-06