Symphony DSP56724/DSP56725 Multi-Core Audio Processors, Rev. 0
21-54
Freescale Semiconductor
External Memory Controller (EMC)
Figure 21-13. GPCM Read Followed by Write
(TRLX = 1, EHTR = 0, Four-Cycle Extended Hold Time on Reads)
21.4.2.3
External Access Termination (LGTA)
External access termination is supported by the GPCM using the asynchronous LGTA input signal, which
is synchronized and sampled internally by the external memory. controller. If, during assertion of LCSx,
the sampled LGTA signal is asserted, it is converted to an internal generation of transfer acknowledge,
which terminates the current GPCM access (regardless of the setting of ORx[SETA]). LGTA should be
asserted for at least one bus cycle to be effective. Note that because LGTA is synchronized, bus termination
occurs two cycles after LGTA assertion, so in case of read cycle, the device still must drive data as long as
LOE is asserted.
The user selects whether transfer acknowledge is generated internally or externally (LGTA) by
programming ORx[SETA]. Asserting LGTA always terminates an access, even if ORx[SETA] = 0
(internal transfer acknowledge generation), but it is the only means by which an access can be terminated
if ORx[SETA] = 1. The timing of LGTA is illustrated by the example in
.
LCLK
LAD
LALE
LCS
n
LBCTL
A
TA
LOE
LCSy
Bus turnaround
Extended Hold
Latched Read Address
Rd. Ad.
Read Data
Wr. Ad. Wr. Da.
Latched Write Addr.