Cypress EZ-USB Series 2100 Service Manual download pdf (Page 323)

EZ-USB TRM v1.9 Appendix C: 8051 Hardware Description C - 27

C.3.6 Multiprocessor Communications

The multiprocessor communication feature is enabled in modes 2 and 3 when the SM2 bit is

set in the SCON SFR for a serial port (SM2_0 for Serial Port 0, SM2_1 for Serial Port 1). In

multiprocessor communication mode, the 9th bit received is stored in RB8_0 (or RB8_1) and,

after the stop bit is received, the serial port interrupt is activated only if RB8_0 (or RB8_1) =

A typical use for the multiprocessor communication feature is when a master wants to send a

block of data to one of several slaves. The master first transmits an address byte that identifies

the target slave. When transmitting an address byte, the master sets the 9th bit to 1; for data

bytes, the 9th bit is 0.

With SM2_0 (or SM2_1) = 1, no slave will be interrupted by a data byte. However, an address

byte interrupts all slaves so that each slave can examine the received address byte to

determine whether that slave is being addressed. Address decoding must be done by software

during the interrupt service routine. The addressed slave clears its SM2_0 (or SM2_1) bit and

prepares to receive the data bytes. The slaves that are not being addressed leave the SM2_0 (or

SM2_1) bit set and ignore the incoming data bytes.

C.3.7 Interrupt SFRs

The following SFRs are associated with interrupt control:

• IE - SFR A8h (Table C-12.)

• IP - SFR B8h (Table C-13.)

• EXIF - SFR 91h (Table C-14.)

• EICON - SFR D8h (Table C-15.)

• EIE - SFR E8h (Table C-16.)

• EIP - SFR F8h (Table C-17.)

The IE and IP SFRs provide interrupt enable and priority control for the standard interrupt

unit, as with the standard 8051. Additionally, these SFRs provide control bits for the Serial

Port 1 interrupt. These bits (ES1 and PS1) are available only when the extended interrupt unit

is implemented (ext_intr=1). Otherwise, they are read as 0.

Bits ES0, ES1, ET2, PS0, PS1, and PT2 are present, but not used, when the corresponding

module is not implemented.

The EXIF, EICON, EIE and EIP registers provide flags, enable control, and priority control

for the optional extended interrupt unit.

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Cypress EZ-USB Series 2100 Service Manual Page 323