NEC Network Controller uPD98502 - Manual (Page 246)

CHAPTER 4 ATM CELL PROCESSOR
246 Preliminary User’s Manual S15543EJ1V0UM
4.4.22 A_UMCMD (UTOPIA Management Interface Command Register)
A_UMCMD selects operation mode of UTOPIA Management Interface. After reset, RISC Core must write this
register to configure UTOPIA Management Interface.
When BM bit is set to ‘0’, it means 8-bit mode and UMD [7:0] pins are valid.
When BM bit is set to ‘1’, it means 16-bit mode. In this case, only half-word-aligned access is accepted.
EM bit is set to ‘1’ only in 16-bit transfer mode. EM bit can change the data alignment as shown below.
V R 4120A
0 31
a b c d
0
a b
15
PHY
EM = 1
V R 4120A
0 31
a b c d
0
a b
15
PHY
EM = 0
Initial value of A_UMCMD is zero.
Bits Field R/W Default Description
31 Reserved R/W 0 Reserved for future use. Write ‘0’s.
30 BM R/W 0 0 = 8-bit transfer mode
1 = 16-bit transfer mode
29 EM R/W 0 0 = data let straight
1 = data let cross
28:3 Reserved R/W 0 Reserved for future use. Write ‘0’s.
2 PR R/W 0 0 = to deassert UMRSTB
1 = to assert UMRSTB to reset PHY device
1:0 MSL R/W 00 00 = UTOPIA Management acts in the Motorola-compatible mode
(DS, R/W, DTACK style)
01 = UTOPIA Management acts in the Intel-compatible mode
(RD, WR, RDY style)
1x = reserved