DP8344 datasheet(57/184 Pages) NSC

57 / 184 page

30 Transceiver (Continued)

When formatting a 3299 address frame the procedure is

the same as for a 3270 frame with RTR 7–2

defining

the address to be transmitted The only bit in TCR which

has any functional meaning in this mode is OWP

which

controls the type of parity required on B1 – B8 Similarly

when the receiver de-formats a 3299 address frame the

received address bits are loaded into RTR 7–2

RTR

1–0

and TSR 2–0

are undefined

The POLL POLLACK and TTAR flags in the Network

Command Flag Register are valid only in 3270 and 3299

(excluding the 3299 address frame) modes These flags are

decodes of their respective coax commands as defined in

Table 3-4 The Data Error or Message End DEME flag

(also in the NCF register) indicates different information

depending on the selected protocol In 3270 and 3299

DEME is set when B10 of the received frame does not

match the locally generated odd parity on bits B2 – B9 of the

received frame

DEME is not part of the receiver error

logic it functions only as a status flag to the CPU These

flags are decoded from the last location in the FIFO and are

valid only when DAV is asserted they are cleared by read-

ing RTR and must be checked before advancing the re-

ceiver FIFO

5250 Modes

The biphase data is inverted in the 5250 protocol relative to

32703299 (see the Protocol sectionIBM 5250) Depend-

ing on the external line interface circuitry the transceiver’s

biphase inputs and outputs may need to be inverted by as-

serting the RIN (Receiver INvert) and TIN (Transmitter

INvert) control bits in TMR

For information on how data must be organized in TCR

and

RTR

for input to the transmitter and how data ex-

tracted from a received frame is organized by the receiver

and mapped into TSR and RTR

see

Figure 3-10

To transmit a 5250 message the least significant 4 bits of

TCR

must first be set up with the correct address and

parity control information The station address field (B4 – B6)

is defined by TCR 2–0

and OWP controls the type of

parity (even or odd) calculated on B4 – B15 and transmitted

as B3 When the 8-bit data byte is written to

RTR

the

resulting composite 12-bit word is loaded into the transmit

FIFO starting the transmitter The same

TCR

contents

can be used for more than one frame of a multi-frame trans-

mission or changed for each frame

The 5250 protocol defines bits B0 – B2 as fill bits which the

transmitter automatically appends to the parity bit (B3) to

TABLE 3-4 Decode of 3270 Coax Commands

Received Word

Flag

Description

B10

B11

RAR

TTAR (Clean Status) Received

ACK

POLLACK Command Received

POLL

POLL Command Received

All flags cleared by reading RTR

TLF9336 – 49

FIGURE 3-10 5250 Frame AssemblyDisassembly Description

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