ATAM862 datasheet(73/110 Pages) ATMEL

73 / 110 page

4554E–4BMCU–05/06

ATAM862-3

Multi-chip link (MCL) – the SSI can also be used as an interchip data interface for use in

single package multi-chip modules or hybrids. For such applications, the SSI is pro-

vided with two dedicated pads (MCL_SD and MCL_SC) which act as a two-wire

chip-to-chip link. The MCL can be activated by the MCL control bit. Should these MCL

pads be used by the SSI, the standard SD and SC pins are not required and the corre-

sponding Port 4 ports are available as conventional data ports.

Figure 23-15. Block Diagram of the Synchronous Serial Interface

23.8.3

General SSI Operation

The SSI is comprised essentially of an 8-bit shift register with two associated 8-bit buffers – the

receive buffer (SRB) for capturing the incoming serial data and a transmit buffer (STB) for inter-

mediate storage of data to be serially output. Both buffers are directly accessable by software.

Transferring the parallel buffer data into and out of the shift register is controlled automatically by

the SSI control, so that both single byte transfers or continuous bit streams can be supported.

The SSI can generate the shift clock (SC) either from one of several on-chip clock sources or

accept an external clock. The external shift clock is output on, or applied to the Port BP40.

Selection of an external clock source is performed by the Serial Clock Direction control bit

(SCD). In the combinational modes, the required clock is selected by the corresponding timer

mode.

The SSI can operate in three data transfer modes – synchronous 8-bit shift mode, a 9-bit

Multi-Chip Link Mode (MCL), or 8-bit pseudo MCL protocol (without acknowledge-bit).

External SSI clocking is not supported in these modes. The SSI should thus generate and has

full control over the shift clock so that it can always be regarded as an MCL bus master device.

All directional control of the external data port used by the SSI is handled automatically and is

dependent on the transmission direction set by the Serial Data Direction (SDD) control bit. This

control bit defines whether the SSI is currently operating in Transmit (TX) mode or Receive (RX)

mode.

Serial data is organized in 8-bit telegrams which are shifted with the most significant bit first. In

the 9-bit MCL mode, an additional acknowledge bit is appended to the end of the telegram for

handshaking purposes (see section “MCL Bus Protocol” on page 77).

8-bit Shift Register

MSB

LSB

Shift_CL

SIC1

SIC2

SISC

Control

STB

SRB

Timer 2 / Timer 3

Output

INT3

I/O-bus

SSI-Control

TOG2

POUT

T1OUT

SYSCL

MCL_SC

MCL_SD

Transmit

Buffer

Receive

Buffer

SCI

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