DSP56303 datasheet(141/292 Pages) FREESCALE

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Operating Modes: Normal, Network, and On-Demand

DSP56303 User’s Manual, Rev. 2

Freescale Semiconductor

7-9

After the first transmit, subsequent transmit values are typically loaded into TXnn by the

ISR (one value per register per interrupt). Therefore, if N items are to be sent from a

particular TXnn, the ISR needs to load the transmit register (N – 1) times. Steps 2c and

2d can be performed in step 2a as a single instruction. If an interrupt trigger event

occurs before all interrupt trigger configuration steps are performed, the event is ignored

and not queued. If interrupts derived from the core or other peripherals need to be

enabled at the same time as ESSI interrupts, step 2f should be performed last.

7.4 Operating Modes: Normal, Network, and On-Demand

The ESSI has three basic operating modes and several data and operation formats. These modes

are programmed via the ESSI control registers. The data and operation formats available to the

ESSI are selected when you set or clear control bits in the CRA and CRB. These control bits are

WL[2–1], MOD, SYN, FSL[1–0], FSR, FSP, CKP, and SHFD.

7.4.1 Normal/Network/On-Demand Mode Selection

To select either Normal mode or Network mode, clear or set CRB[MOD]. In Normal mode, the

ESSI sends or receives one data word per frame (per enabled receiver or transmitter). In Network

mode, 2 to 32 time slots per frame can be selected. During each frame, 0 to 32 data words are

received or transmitted (from each enabled receiver or transmitter). In either case, the transfers

are periodic.

The Normal mode typically transfers data to or from a single device. Network mode is typically

used in time division multiplexed networks of CODECs or DSPs with multiple words per frame.

Network mode has a submode called On-Demand mode. Set the CRB[MOD] for Network mode,

and set the frame rate divider to 0 (DC = $00000) to select On-Demand mode. This submode

does not generate a periodic frame sync. A frame sync pulse is generated only when data is

available to transmit. The frame sync signal indicates the first time slot in the frame. On-Demand

mode requires that the transmit frame sync be internal (output) and the receive frame sync be

external (input). For simplex operation, Synchronous mode could be used; however, for

full-duplex operation, Asynchronous mode must be used. You can enable data transmission that

is data-driven by writing data into each TX. Although the ESSI is double-buffered, only one

word can be written to each TX, even if the transmit shift register is empty. The receive and

transmit interrupts function normally, using TDE and RDF; however, transmit underruns are

impossible for On-Demand transmission and are disabled. This mode is useful for interfacing

with codecs requiring a continuous clock.

Note:

When the ESSI transmits data in On-Demand mode (that is, MOD = 1 in the CRB and

DC[4–0] = $00000 in the CRA) with WL[2–0] = 100, the transmission does not work

properly. To ensure correct operation, do not use On-Demand mode with the WL[2–0]

= 100 32-bit word length mode.

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