P8044AH-R0117 datasheet(43/65 Pages) INNOVASIC

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IA8044/IA8344

Data Sheet

SDLC Communications Controller

March 30, 2010

IA211010112-04

http://www.Innovasic.com

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4.11

Data Clocking Options

The SIU may be clocked in one of two ways, with an external clock or in a self-clocked mode. In

the external clocked mode, a serial clock must be provided on SCLK. This clock must be

synchronized to the serial data. Incoming data is sampled at the rising edge of SCLK. Outgoing

data is shifted out at the falling edge of SCLK.

In the self-clocked mode, the SIU uses a reference clock and the serial data to reproduce the serial

data clock. The reference clock can be an external source applied to SCLK, the IA8044/IA8344’s

internal clock or the Timer 1 overflow. The reference clock must be 16 or 32 the data rate. A

DPLL uses the reference clock and the serial data to adjust the sample time to the center of the

serial bit. It does this by adjusting from a serial data transition in increments of 1/16 of a bit time.

The maximum data rate in the externally clocked mode is 2.4 Mbps in a point-to-point

configuration and 1.0 Mbps in a loop configuration. With a 12-MHz CPU clock, the maximum

data rate in the self-clocked mode with an external clock is 375 Kbps. The maximum data rate in

the self-clocked mode with an internal clock will depend on the frequency of the

IA8044/IA8344’s input clock. An IA8044/IA8344 using a 12-MHz input clock can operate at a

maximum data rate of 375 Kbps.

The Serial mode register Bits [5], [6], and [7] select the clocking option for the SIU (see SMD

4.12

Operational Modes

The SIU operates in one of two modes, AUTO or FLEXIBLE. The mode selected determines

how much intervention is required by the CPU when receiving and transmitting frames. In both

modes, short frames, aborted frames, and frames with CRC errors will be ignored.

AUTO mode allows the SIU to recognize and respond to specific SDLC frames without the

CPU’s intervention. This provides for a faster turnaround time but restricts the operation of the

SIU. When in AUTO mode, the SIU can only act as a normal response secondary station and

responses will adhere to IBM’s SDLC definitions.

When receiving in the AUTO mode, the SIU receives the frame and examines the control byte. It

will then take the appropriate action for that frame. If the frame is an information frame, the SIU

will load the receive buffer, interrupt the CPU and make the required response to the primary

station. The SIU in AUTO mode can also respond to the following commands from the primary

station:

RR (Receive ready)

RNR (Receive Not Ready)

REJ (Reject)

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