GS9021 datasheet(12/26 Pages) GENNUM

12 / 26 page

521 - 65 - 05

The IN/OUT bit has no effect on writes to the error flags. IN/

OUT is a control bit used to determine if the flags read from

the flag port during flag port read cycles represent

incoming or outgoing EDH flags. If this bit is set HIGH, all

subsequent reads are from the incoming EDH packet. If this

bit is set LOW, then all subsequent reads are from the

updated outgoing packet. When the IN/OUT bit is written to,

the value remains latched until it is reprogrammed. The IN/

OUT bit is set LOW upon reset of the chip.

3.9.2 Read Mode

When the F_R/W pin is HIGH, the flag port is in read mode

and the FL[4:0] pins are configured as outputs. The data

present on the FL[4:0] output pins, as controlled by the

S[1:0] pins, is summarized below.

Note that the 15 error flags can be read from the incoming

or outgoing EDH packet (see IN/OUT control bit above).

However, the EDH_CHKSM flag available on pin FL4 when

S[1:0] = 11 is only valid if IN/OUT is LOW. Also, the APV

and FFV bits available on pins FL[3:2] when S[1:0] = 11 are

only valid when IN/OUT is HIGH (that is, the validity bits are

always read from the incoming EDH packet). The S bit is

available regardless of the state of the IN/OUT bit.

3.9.3 Flag Port READ/WRITE Timing

Figure 5a shows a FLAG PORT write cycle followed by a

FLAG PORT read cycle and illustrates the read/write timing

requirements.

A write cycle is initiated by changing the F_R/W signal from

HIGH to LOW.

The first time the device samples the F_R/W LOW (at t0) it is

instructed to stop driving the FL[4:0] pins. On each

subsequent rising clock edge (and F_R/W LOW) the device

latches in the data present on S[1:0] and FL[4:0] (at t1, t2, t3

and t4). In this example, the S[1:0] pins begin at "00" and

are incremented each clock cycle to update all the error

flags, validity bits, and the IN/OUT control bit. Note that if a

write cycle is performed to update, say the FF error flags

(S[1:0] = 00), only the FF flags are updated, and the others

are unaffected.

A delay time, tFDIS, is necessary to change the FL[4:0] pins

from output mode to input mode as defined in the AC timing

table (See Fig.5b). The external controller can begin to

drive the FL[4:0] bus after this delay time. A simple way to

allow for this is to wait one clock cycle before starting to

drive the FL[4:0] port and thus prevent bus contention (but

set the S[1:0] inputs when F_R/W goes LOW so the flags

are not unintentionally affected).

At t5, the F_R/W pin is sampled HIGH, indicating a read

operation. Also at this time, the device reads in the

information on the S[1:0] pins. Upon sampling a read

operation, the device will begin driving the FLAG PORT

after a delay, tFEN, (see Fig. 5c), with invalid data. The

requested information is output on the FL[4:0] pins on the

subsequent clock, t6, plus an output delay time, (see AC

timing table and Fig. 2). That is, there is a one clock latency

between sampling of the S[1:0] pins and when the

corresponding output information is presented on the

FL[4:0] pins. In this example, the S[1:0] pins begin at "00"

and are incremented each clock cycle to read all the error

flags, EDH_CHKSM, validity, and S bits.

The FLAG PORT is synchronous to the clock pin (PCLKIN)

and hence adequate setup and hold times must be

provided as indicated in the AC timing information and Fig.

1. FLAG PORT read/write cycles, relative to the data stream,

should take place as outlined in section 5.3 (HOST

INTERFACE READ/WRITE TIMING)

3.10 CRC_MODE and FLAG_MAP Mode

A common configuration is to have an input EDH chip that

checks for errors at the input of a piece of equipment,

followed by a processing block that manipulates the data,

followed by an output EDH chip that updates the CRC

values in the EDH packet before the data exits the

equipment. Because the processing block changes the

data values, the CRC values in the EDH packet no longer

represent the data stream. The output EDH chip updates

Write Mode, F_R/W = 0

S[1:0]

FL4

FL3

FL2

FL1

FL0

FF UES

FF IDA

FF IDH

FF EDA

FF EDH

AP UES

AP IDA

AP IDH

AP EDA

AP EDH

ANC

UES

ANC

IDA

ANC

IDH

ANC

EDA

ANC

EDH

IN/OUT

APV

FFV

Read Mode, F_R/W = 1

S[1:0]

FL4

FL3

FL2

FL1

FL0

FF UES

FF IDA

FF IDH

FF EDA

FF EDH

AP UES

AP IDA

AP IDH

AP EDA

AP EDH

ANC UES

ANC

IDA

ANC

IDH

ANC

EDA

ANC

EDH

EDH_

CHKSUM

APV

FFV

LOGIC OPR

HOST BIT

CRC_MODE

FLAG_MAP

GS9021 Datasheet(PDF) 12 Page - Gennum Corporation

GS9021 Datasheet(HTML) 12 Page - Gennum Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Datasheet Download

Link URL