C8051F360/1/2/3/4/5/6/7/8/9
11. Multiply And Accumulate (MAC0)
The C8051F36x devices include a multiply and accumulate engine which can be used to speed up many
mathematical operations. MAC0 contains a 16-by-16 bit multiplier and a 40-bit adder, which can perform
integer or fractional multiply-accumulate and multiply operations on signed input values in two SYSCLK
cycles. A rounding engine provides a rounded 16-bit fractional result after an additional (third) SYSCLK
cycle. MAC0 also contains a 1-bit arithmetic shifter that will left or right-shift the contents of the 40-bit accu-
mulator in a single SYSCLK cycle. Figure 11.1 shows a block diagram of the MAC0 unit and its associated
Special Function Registers.
MAC0 A Register
MAC0AH MAC0AL
MAC0 B Register
MAC0BH MAC0BL
MAC0MS
MAC0FM
16 x 16 Multiply
1
0
0
40 bit Add
MAC0OVR
MAC0 Accumulator
MAC0ACC3 MAC0ACC2 MAC0ACC1
MAC0ACC0
1 bit Shift
Rounding Engine
Flag Logic
MAC0SC
MAC0SD
MAC0CA
MAC0SAT
MAC0FM
MAC0MS
MAC0CF
MAC0STA
Figure 11.1. MAC0 Block Diagram
11.1. Special Function Registers
There are thirteen Special Function Register (SFR) locations associated with MAC0. Two of these regis-
ters are related to configuration and operation, while the other eleven are used to store multi-byte input
and output data for MAC0. The Configuration register MAC0CF (SFR Definition 11.1) is used to configure
and control MAC0. The Status register MAC0STA (SFR Definition 11.2) contains flags to indicate overflow
conditions, as well as zero and negative results. The 16-bit MAC0A (MAC0AH:MAC0AL) and MAC0B
(MAC0BH:MAC0BL) registers are used as inputs to the multiplier. The MAC0 Accumulator register is 40
bits long, and consists of five SFRs: MAC0OVR, MAC0ACC3, MAC0ACC2, MAC0ACC1, and
MAC0ACC0. The primary results of a MAC0 operation are stored in the Accumulator registers. If they are
needed, the rounded results are stored in the 16-bit Rounding Register MAC0RND
(MAC0RNDH:MAC0RNDL).
Rev. 1.0
MAC0HO
MAC0Z
MAC0SO
MAC0N
MAC0 Rounding Register
MAC0RNDH MAC0RNDL
117
SILABS [ SILICON LABORATORIES ]
