Functional Description
Reaction of the ISAC-S
In the following various possible actions to be taken according to § 5.8.5 parts a) through c)
are discussed separately.
a) There are different types of undefined frames:
1) I-frame which is not command
an ISTA: PCE-interrupt is generated
2) S-frame with bits 8-5 in Octet 4 = 0 an ISTA: PCE-interrupt is generated
3) A-frame with bits 4-1 in octet 4
equal to "1101" (selective reject)
an ISTA: PCE is generated
4) Frame with bits 2-1 in octet 4 equal
to "11" but control field not contained
in ISTA: RME interrupt;
the control field can be read afterwards in
RHCR (after having checked for invalid
frame condition).
5) SABME, UI, DISC, not a command,
DM, UA, FRMR not a response
ISTA: RME interrupt;
the control field can be read afterwards in
RHCR, the C/R-bit in the SAPR-register
(after having checked for invalid frame
condition).
b) If the length of the frame is too small 1.1.1b) applies and the frame is invalid. Therefore
incorrect length can only mean:
1) S-frame with more than 6 octets
an ISTA:PCE-interrupt is generated; the
contents of the additional octets is discarded.
2) Undefined frames with 5 octets,
bits 2-1 in octet 4 not being equal
to "11" (e.g. modulo 8 S-frame)
an ISTA:PCE-interrupt is generated
3) SABME, BM, DISC, UA-frame
with more than 5 octets
after ISTA:
RME and identifying the frame by RHCR the
RSTA:RDA bit is 1 if the frames had more
than 5 octets and 0 if they had exactly 5 octets.
4) A FRMR with not exactly 10 octets After a RME and identifying FRMR by
reading RHCR-register, the software has to
read RBCH, RBCL. If OV = 1 or
RBC11-RBC0 = 0 … 101 then the FRMR did
not have exactly 10 octets.
c) An invalid N(R) is one that does not meet the condition
V(A) < N(R) < V(S)
This condition is automatically checked within the device and in the case of an invalid
N(R) an ISTA:PCE-interrupt is generated. An S-field response is done by the ISAC-S
in all prescribed cases of invalid N(R) automatically.
Semiconductor Group
127
INFINEON [ Infineon ]
