10 Mbps ARCNET (ANSI 878.1) Controller with 2Kx8 On-Board RAM
Datasheet
BIT
BIT NAME
SYMBOL
DESCRIPTION
1,0 Reconfiguration
Timer 1, 0
RCNTM1, These bits are used to program the reconfiguration timer as
0
a function of maximum node count. These bits set the time
out period of the reconfiguration timer as shown below. The
time out periods shown are for 10 Mbps.
Time Out
Period
RCNTM1 RCNTM0
Max Node Count
Up to 255 nodes
Up to 64 nodes
Up to 32 nodes
Up to 16 nodes
0
0
1
1
0
1
0
1
210 mS
52.5 mS
26.25 mS
13.125 mS*
Note*: The node ID value 255 must exist in the network for
13.125 mS timeout to be valid.
Table 6.14 - Bus Control Register
BIT
BIT NAME
SYMBOL
DESCRIPTION
7
16 Bit Access
W16
This bit is used to Disable/Enable the 16 bit access. It
influences both CPU cycle and DMA cycle. W16= 0: Disable
(Default); W16= 1: Enable
6
5
Reserved
This bit is undefined.
Internal Terminal
Counter Enable;
Re-Trigger mode
ITCEN/
RTRG
The function of this bit is mode dependent. ITCEN is for Non-
Burst or Burst mode. RTRG is for the two Programmable-
Burst modes.
ITCEN = 0: Terminate the DMA only by External TC. ITCEN
= 1: Terminate the DMA by Internal or External TC.
RTRG = 0: External Re-Trigger mode; Negated DREQ pin is
Re-asserted by falling edge of nREFEX pin. RTRG = 1:
Internal Re-Trigger mode; Negated DREQ pin is Re-asserted
by timeout of internal gate timer (350ns/750ns).
4
Terminal Count
Bit 8
TC8/
The function of this bit is mode dependent. TC8 is for Non-
burst or burst mode. RSYN and GTTM are for the two
Programmable-Burst modes. RSYN is for External Re-
Trigger mode. GTTM is for internal Re-Trigger mode.
RSYN/
GTTM
Refresh
Synchronous
Gate Time
Non-burst or burst mode:
TC8: Bit 8 (MSB) of 9 bit Terminal Count setting register.
The other 8 bits are in the DMA Count register. Terminal
Count setting register is ignored when ITCEN = 0.
Programmable-Burst and External Re-Trigger mode:
RSYN = 0: DMA is started Immediately.
RSYN = 1: DMA is started after Refresh execution.
Programmable-Burst and Internal Re-Trigger mode:
GTTM = 0: Gate Time is 350nS (min)
GTTM = 1: Gate Time is 750nS (min)
Revision 02-27-06
Page 44
SMSC COM20022I 3V
DATASHEET
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