NEC UPD98413 User Manual page 73

(f) FCS check
The µ PD98413 executes an FCS operation (CRC-32 or CRC-CCIT operation) on the entire packet data and then
performs an FCS check. The user can select between a 32-bit FCS and a 16-bit FCS for the FCS check. The
polynomial for each is as follows:
32-bit FCS (CRC-32):
2 4
g(x) = 1 + x + x + x + x
16-bit FCS (CRC-CCIT):
5 12 16
g(x) = 1 + x + x + x
After performing the FCS check, the µ PD98413 sends the packet stripped the FCS or not stripped, which is the
setting by the FCSPAS bit of the MDPOSR register, to the POS interface. When the FCS is not stripped, the
µ PD98413 places the results of the FCS operation in the FCS field. If no FCS error occurs, the value in the FCS
field is zero.
If an FCS error occurs, this is reported by asserting the RERR pin at the end of the packet. The µ PD98413 also
increments the FCS error counter and indicates it by the interrupt.
The FCS check function is optional and it may be disabled by the FCSM bit of the MDPOSR register.
(g) Performance monitors
The µ PD98413 supports the following receive error handling and performance counters.
described below. All the counters are 32-bit counters.
• Receive valid packet counter
• Receive abort packet counter
• Receive Address error counter
• Receive FCS error counter
• Receive FIFO overflow counter
• Receive short size packet counter
• Receive long size packet counter
Receive valid packet counter
Upon receiving a packet without an error, the µ PD98413 increments the receive packet counter. This counter is
selectable in units of packets or bytes, and it may be selected by the VPCRM bit of the MDCNTR register.
Receive abort packet counter
Upon receiving an abort packet (which ends with abort sequence 7D-7E), the µ PD98413 increments the receive
abort packet counter.
Receive Address error counter
Upon receiving a packet, the µ PD98413 detects the Address and control fields in the packet (first byte of the
POS packet) and checks it. If the value in the Address field of the packet is not FFh or the control field is not 03h,
the packet is handled as an address error packet, and the address error counter is incremented.
Receive FCS error counter
Upon detecting an FCS error, the µ PD98413 increments the FCS error counter.
CHAPTER 3 FUNCTIONAL OUTLINE
5 7 8 10 11 12 16
+ x + x + x + x + x + x
PRELIMINARY
22 23 26 32
+ x + x + x + x
Each counter is
NEC confidential and Proprietary
73