DSPIC30F2011AT-30ESLASHPF datasheet(134/228 Pages) MICROCHIP

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DS70117F-page 132

18.3.18

SLOT STATUS BITS

The SLOT<3:0> status bits in the DCISTAT SFR indi-

cate the current active time slot. These bits will corre-

spond to the value of the frame sync generator counter.

The user may poll these status bits in software when a

DCI interrupt occurs to determine what time slot data

was last received and which time slot data should be

loaded into the TXBUF registers.

18.3.19

CSDO MODE BIT

The CSDOM control bit controls the behavior of the

CSDO pin during unused transmit slots. A given trans-

mit time slot is unused if it’s corresponding TSEx bit in

the TSCON SFR is cleared.

If the CSDOM bit is cleared (default), the CSDO pin will

be low during unused time slot periods. This mode will

be used when there are only two devices attached to

the serial bus.

If the CSDOM bit is set, the CSDO pin will be tri-stated

during unused time slot periods. This mode allows mul-

tiple devices to share the same CSDO line in a multi-

channel application. Each device on the CSDO line is

configured so that it will only transmit data during

specific time slots. No two devices will transmit data

during the same time slot.

18.3.20

DIGITAL LOOPBACK MODE

Digital Loopback mode is enabled by setting the

DLOOP control bit in the DCISTAT SFR. When the

DLOOP bit is set, the module internally connects the

CSDO signal to CSDI. The actual data input on the

CSDI I/O pin will be ignored in Digital Loopback mode.

18.3.21

UNDERFLOW MODE CONTROL BIT

When an underflow occurs, one of two actions may

occur depending on the state of the Underflow mode

(UNFM) control bit in the DCICON1 SFR. If the UNFM

bit is cleared (default), the module will transmit ‘0’s on

the CSDO pin during the active time slot for the buffer

location. In this Operating mode, the Codec device

attached to the DCI module will simply be fed digital

‘silence’. If the UNFM control bit is set, the module will

transmit the last data written to the buffer location. This

Operating mode permits the user to send continuous

data to the Codec device without consuming CPU

overhead.

18.4

DCI Module Interrupts

The frequency of DCI module interrupts is dependent

on the BLEN<1:0> control bits in the DCICON2 SFR.

An interrupt to the CPU is generated each time the set

buffer length has been reached and a shadow register

transfer takes place. A shadow register transfer is

defined as the time when the previously written TXBUF

values are transferred to the transmit shadow registers

and new received values in the receive shadow

registers are transferred into the RXBUF registers.

18.5

DCI Module Operation During CPU

Sleep and Idle Modes

18.5.1

DCI MODULE OPERATION DURING

CPU SLEEP MODE

The DCI module has the ability to operate while in

Sleep mode and wake the CPU when the CSCK signal

is supplied by an external device (CSCKD = 1). The

DCI module will generate an asynchronous interrupt

when a DCI buffer transfer has completed and the CPU

is in Sleep mode.

18.5.2

DCI MODULE OPERATION DURING

CPU IDLE MODE

If the DCISIDL control bit is cleared (default), the mod-

ule will continue to operate normally even in Idle mode.

If the DCISIDL bit is set, the module will halt when Idle

mode is asserted.

18.6

AC-Link Mode Operation

The AC-Link protocol is a 256-bit frame with one 16-bit

data slot, followed by twelve 20-bit data slots. The DCI

module has two Operating modes for the AC-Link pro-

tocol. These Operating modes are selected by the

COFSM<1:0> control bits in the DCICON1 SFR. The

first AC-Link mode is called ‘16-bit AC-Link mode’ and

is selected by setting COFSM<1:0> = 10. The second

AC-Link mode is called ‘20-bit AC-Link mode’ and is

selected by setting COFSM<1:0> = 11.

18.6.1

16-BIT AC-LINK MODE

In the 16-bit AC-Link mode, data word lengths are

restricted to 16 bits. Note that this restriction only

affects the 20-bit data time slots of the AC-Link proto-

col. For received time slots, the incoming data is simply

truncated to 16 bits. For outgoing time slots, the 4 LSbs

of the data word are set to ‘0’ by the module. This trun-

cation of the time slots limits the A/D and DAC data to

16 bits but permits proper data alignment in the TXBUF

and RXBUF registers. Each RXBUF and TXBUF regis-

ter will contain one data time slot value.

18.6.2

20-BIT AC-LINK MODE

The 20-bit AC-Link mode allows all bits in the data time

slots to be transmitted and received but does not main-

tain data alignment in the TXBUF and RXBUF

registers.

The 20-bit AC-Link mode functions similar to the Multi-

Channel mode of the DCI module, except for the duty

cycle of the frame synchronization signal. The AC-Link

frame synchronization signal should remain high for 16

CSCK cycles and should be low for the following

240 cycles.

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